After minor back surgery brought an abrupt end to his 2013 campaign, there was a feeling of uncertainty surrounding Andy Murray when he returned to the ATP Tour at the start of the season.

The 26-year-old's preparation for the Australian Open was less than stellar, but the two-time Grand Slam champion played without expectation in Melbourne before eventually succumbing to a supreme display from Roger Federer in four sets at the quarter-final stage.

However, after failing to reach the final in the three tournaments that followed the opening major of the year, can Murray be content with a clean bill of health, or should he be concerned by his failure to progress in matches that he would have been expected to come through in fairly comfortable fashion?

With Murray openly admitting that he had little chance of achieving his first triumph in Australia, he had seemingly given himself a free pass to ease back into the rigours of the sport, and an appearance in the latter stages would be one to take heart from as he looked to defend several thousand ranking points in the first half of the year.

But despite losing to Federer in the last eight, his performance suggested that he had settled back into life on the tour and that he was ready to resume his pursuit for a third major, while also attempting to overhaul Rafael Nadal and Novak Djokovic in the world rankings.

There were also signs during Great Britain's Davis Cup encounter with USA that the competitive nature of the Scot had never been stronger, and after helping his team to a tie with Italy, all eyes were on Murray to see if he could transfer his form back onto the tour when making an appearance at the indoor tournament in Rotterdam.

Murray began strongly enough against Edouard Roger-Vasselin, a player that he had previously defeated twice, but he came under fierce pressure from young Austrian Dominic Thiem, whose aggressive play suggested a change in how the up-and-comers in the men's game are attempting to make a statement against the world's best.

Thiem's assault from the baseline failed to get the job done against Murray, but the Scot's struggles only gave encouragement to an in-form Marin Cilic, who made light work of the Brit in a one-sided encounter in which Murray failed to cope with the power of the tall Croatian.

With 500 ranking points up for grabs, Murray moved on to a first-time appearance in Acapulco, but whether it was a lack of mobility or failure to acclimatise to the conditions, the right-hander twice had to come from a set deficit to get through to a semi-final showdown with Grigor Dimitrov.

The match not only offered valuable points but also an opportunity to maintain his undefeated streak against a man tipped for the top of the game, but despite taking the opener, Dimitrov roared back to get the better of Murray in two tie-breaks as the 26-year-old failed to make use of his superior experience.

Positives could be taken from Mexico, but like in Rotterdam, Murray had ultimately been overpowered in a decisive match, and ahead of a vital month in the States, he needed a big showing in Indian Wells to ease the pressure of his title defence in Miami.

Murray was soon in trouble against Lukas Rosol, the conqueror of Nadal at Wimbledon in 2012, but he eventually outclassed the Czech before enduring similar difficultly in getting past Jiri Vesely, another youthful hitter who is tipped to have an impact in tennis in years to come.

Milos Raonic awaited Murray in the last 16 in a match that the Brit needed to win to defend his points from 2013, but despite withstanding the power of the Canadian for the first set-and-a-half, Murray wilted alarmingly during the pressure moments of the tie that saw him exit a tournament that had offered him the opportunity to keep the pressure on the players in front of him in the standings.

However, the defeat leaves Murray requiring a huge performance in Miami to avoid falling to number eight in the world rankings ahead of what is always a testing couple of months on the clay, with his chances of defending his Wimbledon title growing ever difficult while he sits a long way adrift of Nadal, Djokovic and Stanislas Wawrinka.

While Murray's ranking position is one of genuine concern, perhaps his struggle to adapt to the evolving power tactics used in the sport is one that will cause the most worries, with Murray's reliance on waiting for a mistake from his opponent one that may not prove so effective if opponents continue to seize the initiative against him in future contests.

Coach Ivan Lendl will reacquaint himself with Murray in Florida, and his first task could be to alter the mental approach of a player that he turned into a Grand Slam champion or Murray may face the prospect of a prolonged spell outside of the top four.

Murray has reason to be fairly pleased with how he has fared since the start of the year, but as he admitted after his defeat to Raonic, his current level isn't good enough and an improvement is needed in the coming weeks.