There's something deeply saddening about watching a once master of his or her's craft struggling to produce the standards that had once come so unnervingly naturally.

Fourteen-time Major winner Tiger Woods is living that nightmare, while defeats to even the most average of opponents have become an all too frequent occurrence for the great Roger Federer.

It's even something that the greatest of them all - Muhammad Ali - could not escape. On October 2, 1980, a 38-year-old Ali took to a temporary arena at Caesars Palace in Las Vegas, where he would face former sparring partner Larry Holmes.

What followed was brutal. Ali, a shell of his former all-conquering self, had no reflexes, no defence, no punch and no legs. Holmes dominated every second of every round until Ali's corner called time on proceedings in the 10th.

Wayne Rooney, a self-confessed boxing enthusiast himself, may not be ready to throw in the towel like Ali's trainer Angelo Dundee was forced to do on that evening 35 years ago, but the Manchester United skipper is certainly on the ropes.

A recent BBC Sport documentary highlighted just how mature Rooney, who turned 30 earlier this month, has become. A father of two young boys and with a third child on the way, we were granted unprecedented access to Rooney the family man.

Yet, from a purely sporting perspective, the hour-long broadcast served mainly to remind viewers just how fantastic a player Rooney was (note the deliberate use of past tense).

We saw footage of Euro 2004 - a tournament that England looked a good bet to win until Rooney was struck down by the then fashionable broken metatarsal during the quarter-final against hosts Portugal. Prior to that, the 18-year-old terrorised the French, Swiss and Croatian defences, scoring four goals to earn himself a place in UEFA's Team of the Tournament.

On the back of that, Rooney, a boyhood Evertonian, left Goodison Park for Manchester United, for whom he would mark his debut with a Champions League hat-trick against Fenerbahce. It set the tone for the next few years.

Rooney was a bull, built like a man at 16. He was quick, strong, powerful, aggressive and could score all manner of goals - important ones to boot.

As David Moyes, who managed the Croxteth-born striker first at Everton and then again at United, noted in 2013: "Some of the things he used to do in training, we would stand back and look at each other as if to say, 'How did he do that?' He was and is an exceptional talent.

"Wayne was brilliant in some of the stuff he did. He was football mad. Every training session he would run out, volleying the ball everywhere. Staff would exchange glances that suggested, 'Can you believe that?'

"Wayne was the last of the classic street footballers. As a 16-year-old he could have left training and then gone out into the street with his pals, thinking nothing of it. You would see him in the street, hitting a ball against the walls."

What we see now is a shadow of that player Moyes recalls so fondly. It might not quite be an Ali vs. Holmes situation just yet, but at the same time it isn't a million miles away either. This is not simply a case of a loss of form, it's gone on too long for that.

In 2012, Sir Alex Ferguson, who rarely called it wrongly when it came to judging if a player's better days were behind him, believed that Rooney was unable to score the amount of goals needed to regain the title from Manchester City. He subsequently signed Robin van Persie and the Dutchman almost single-handedly fired United to a 20th crown, while United's number 10 ended the campaign banished from the squad. Had he not retired, Ferguson would have almost certainly sold Rooney to the highest bidder in 2013.

Ferguson departed and Rooney remained, yet even the Scot's departure has been unable to stoke the flames.

This season there has been a 1,000-minute Premier League goal drought and while there will be those that quite rightly point to the fact that he is still currently United's leading goalscorer with six, it's worth noting that those goals have come against Club Brugge, Sunderland, Ipswich Town and Everton - with the greatest of respect, not stellar opposition. For England he's netted against San Marino and Switzerland, both times from the penalty spot.

The goals - or lack of - are not the most worrying aspect, though. Rooney has always been a player that will go a number of games without finding the net, just as he did during the 2006-07 campaign as eight outings passed without the net being bulged. Scoreless runs of six or seven matches have been the norm and were frequently followed by a clinical spree.

Instead, it's his all-round contribution that should be the cause of major concern for United manager Louis van Gaal. In lean spells of yesteryear Rooney still provided for the team, be it with assists or just generally setting the tone.

During the recent Manchester derby - a fixture in which Rooney is the all-time leading goalscorer - he had no shots and made no key passes, according to statisticians Opta. In fact, there was only one touch in the City penalty area and that didn't come until the 70th minute. As for passes, his 55% completion rate was a United low - even goalkeeper David de Gea walked off with 69% to his name. Also, the 28 times that he lost possession was more than any other player on the pitch.

Of course this is only reflective of one game and players are entitled to have bad days, but the figures from the Man City clash have become the rule rather than exception. For example, against Swansea City he had less touches in the first half than United keeper Sergio Romero, while in United's last Champions League outing in Moscow only De Gea touched the ball on fewer occasions than Rooney (40). Away at Aston Villa and playing as a centre-forward, he failed to register a shot on or off target.

The stats don't lie and neither does what can be seen with the naked eye. A heavy first touch will often play him into trouble, while he is no longer able to harass defenders in the abrasive manner which he once did. There's even less bookings and fouls committed. It's as if there isn't as much fire in the belly, or perhaps the legs simply won't allow him to get there any more.

For good measure, in his most recent outing against Crystal Palace, Rooney chased an inch perfect through-ball from Anthony Martial as if he were wading through marshland. Instead of taking the ball in his stride and getting a shot away, it simply ran through to Palace goalkeeper Wayne Hennessey, who collected with ease. Had the roles have been reversed, it would have taken a brave person to bet against the sprightly, exciting French youngster bulging the back of the net, just as Rooney would have done once upon a time.

The fact that Van Gaal has used him in midfield, out wide, up front and in the number 10 position already this term is further indicative of Rooney's struggles. Had he excelled in any of those roles, surely he would have remained there?

Regardless of the armband, Van Gaal's persistence is certainly reason for head scratching. Let's not forget this is a manager that once informed a startled Bayern Munich squad that he had necessary-sized testicles to put any player on the bench, regardless of their status, by dropping his trousers in front of them. He hasn't been shy of omitting other United players for what he perceives to be underperformance either, just ask fan favourite Ander Herrera.

Van Gaal was also ruthless with Van Persie and Radamel Falcao in the summer and it would be extremely tough for even the most expensive of defence lawyers to put together a legitimate case that argues Rooney has been better this term than the Dutchman or the Colombian were in 2014-15.

Ask yourself, where would Rooney - mocked by Greater Manchester Police on Twitter last night as being a missing person - fit at the other top clubs in Europe? At Bayern Munich? At Barcelona? Would he even break into the teams at Man City or Arsenal? Currently he'd struggle to make the bench, which makes his seemingly untouchable status at Old Trafford - a ground so used to success - all the more odd.

Nevertheless, it would be naive, churlish and downright inaccurate to suggest that Rooney is the sole reason behind United's fun-free and turgid displays. He hasn't instilled the safety-first approach that seems to have left each player fearful of making a mistake, as Paul Scholes noted last week.

It's because of that mentality that United's 3,246 sideways passes is the second highest in the Premier League, while they top the table as far as backward passes (1,041) are concerned. Although, were the centre-forward more mobile and able to stretch a defence, the space created would surely lead to more positive passing. The whole team - not just Rooney - have not scored in the last three matches.

Those statistics highlight that dropping Rooney would not provide an immediate fix, but it would at least mark the start of a necessary process.

In truth, the fact that he is leading both United's and England's attack is as much to do with a lack of alternatives as it is to do with his excellence, although the likes of Martial, Harry Kane, Theo Walcott, Jamie Vardy, and Daniel Sturridge (if he could remain fit) are slowly starting to apply some serious pressure.

There is, of course, one big mitigating circumstance as to why this country's once shining light is fading fast. Having broken into the Everton team at the age of 16 and stayed there, Rooney has averaged almost 50 games a season for club and country since then. To put that into some context, at the end of United's Premier League title and Champions League-winning 2007-08 campaign, Rooney, still just 22, had already been exposed 266 club games and been capped 42 times by his country - an incredible amount of football for one so young.

While his birth certificate may read born in 1985, in footballing terms, he has the body (and possibly mind) of a 34 or 35-year-old and his performances are justifying that opinion. He is a veteran in the guise of a 30-year-old. While traditionally players are said to be at the peak of their powers somewhere between the years of 27 and 32, Rooney's vintage spell, due to the fact that he made his debut and played so regularly while others his age were sitting their GCSEs and A-levels, came early.

Some suggest that Rooney's talent warrants more, that he should ludicrously have worked his way into the same stratosphere as the freaks of nature that are Cristiano Ronaldo and Lionel Messi. But, to say that his career has been in any way unfulfilled would be both incorrect and unfair.

He's won the Premier League five times, the League Cup twice (scoring in both finals) and hoisted the Champions League trophy high above his head. He's also scored in another Champions League final, been voted the PFA Players' Player of the Year once and named in the Team of the Year three times. Already England's leading goalscorer of all time, he is 14 short of surpassing Sir Bobby Charlton as United's record goalscorer. In 2012, his overhead kick against Man City was voted the greatest goal of the Premier League era. He may have his critics on the international stage, but at club level, it's difficult to see what more he could have done to satisfy the masses.

Such accolades once felt inevitable and that they would never stop coming, but the future is now much more uncertain. Former Man United defender Danny Higginbotham recently claimed in conversation with Sports Mole that to prolong his career, Rooney may need to take a leaf out of Ryan Giggs's book.

"If you look at someone like Ryan Giggs, he played for Manchester United from a young age as well and played a lot of games. When he got older, he changed the way he played the game. He had electric pace and even towards the end of his career he still had that sharp burst," he said.

"When he was younger he could run from one end of the pitch to the other in almost a sprinter's time. Whereas, as he got older, he had to change his game and ended up being a central midfielder at times. Maybe Wayne Rooney needs to change his game. You hear some people saying that he could play midfield because he doesn't have that same dynamism that he had a few years ago. Great players are able to adjust as they get older - it's all about how you can do that."

Whether Rooney's body allows for such a dramatic transformation to take place, only time will tell. Not over indulging during the summer break would help, but even so, it may still be too late. Unlike Giggs, Rooney was not blessed with an athletic physique and upon his return to pre-season training, United's medical team have been known to find evidence that a good time had been had.

Footballers in this day and age, and particularly those over the age of 30, have to make sacrifices and keeping relatively fit during the off-season is one of them.

Not only that, while Rooney was a highly effective footballer in his pomp, you wouldn't put him in the same bracket as Giggs or another United legend - the all of a sudden vocal Scholes - when it comes to technical ability. Adaption in the autumn of their careers seemed to come so easily for those two, who played the game as if they had a map in front of them and were often two or three passes ahead of the rest. Remember, Scholes was not given the nickname 'Sat Nav' by Rio Ferdinand for no reason.

Is Rooney finished at the very top? The next few months will likely answer that, but right now the end does look nigh. After all, the sands of time wait for nobody, as Woods, Federer and Ali will all testify.