Following Andy Murray's dogged improvement to turn himself from onlooker to two-time Grand Slam champion, the Brit looked to be heading for the world's number one spot. However, defeat to Stanislas Wawrinka on Thursday night denied him the chance to defend his first title.

Roger Federer's decline looks to have well and truly set in and although Novak Djokovic is as strong as ever, Nadal's recent injury concerns raised questions over whether he could perform at any other Slam than the French. His performances in reaching the semi-finals of Flushing Meadows this year have put to bed doubts over his ability, but of the remaining three players, can any one of them beat him to the title?

Richard Gasquet:

The first man to have a shot will be France's Richard Gasquet. With his springy, serve and volley style of tennis, on his day Gasquet can be a challenge for anyone, but into the closing stages of a tournament - this is only his second Slam semi-final - it is uncertain whether he has the fitness to last.

Indeed, Gasquet's last two matches here have gone all the way. In round four he overturned a 2-1 deficit to edge past Milos Raonic, with three of the sets going to tie-break. If that was not hard enough, he then had to battle against the momentum of David Ferrer. Gasquet was two sets up and cruising before Ferrer levelled it, with the Frenchman finally claiming the win in one of the best sets he has played in his career.

His reward is an even tougher test against Nadal with a day to rest. History does not favour him either, with Nadal winning all 10 matches they have played on the professional tour. The two five-setters will have done one of two things: either Gasquet will be too tired to put up enough of a fight, or his new-found determination will drag him through another marathon clash. It looks to be one step too far, though.

Stanislas Warwinka:

If Stanislas Wawrinka is to get his chance of taking on the rampant Spaniard, he just has to get through the world number one Novak Djokovic first. There is a lot to be said for momentum in tennis, and the Swiss will have got a great deal from his thumping straight-sets win over defending champion Murray. If he can perform like that against Murray, then there is no reason to suggest that he cannot against Djokovic and potentially Nadal.

What he has in his favour is the short amount of time he has so far spent on court. In his five matches so far, Wawrinka has dropped just two sets, which will boost his confidence and will make sure that he is in top shape for the Djokovic clash. His aggressive play against the top seeds - as shown against Murray - is a real threat to anyone.

Should he get past Djokovic, then Wawrinka could pose a real threat to Nadal. The Spaniard is used to bossing points from the baseline, but will come up against a player who has no fear against the world's best.

Novak Djokovic:

The Serb is always going to be in a discussion about favourites for a Grand Slam. He is still the world number one and on his day can still make any player look silly. While many players - including Nadal at times - struggle for fitness towards the end of a tournament, Djokovic comes into his own. He is the pinnacle of human fitness and almost seems to get stronger with each passing round.

In order to have a shot at Nadal - should the Spaniard beat Gasquet - Djokovic first has to see off Wawrinka. While Federer, Nadal and Murray have all shown the tendency to lose to lower-ranked players in Slams, the same cannot be levelled at the Serb. Murray complained about a lack of motivation in his defeat to the Swiss, but Djokovic seems able to prepare equally for every contest.

Djokovic and Nadal have faced each other 36 times in total, with the Spaniard leading 21-15. However, the Serb has tended to have the edge on hard courts. Indeed, their last meeting at Flushing Meadows was in the 2011 final, which Novak won in four sets. Should they meet again, then Nadal would take comfort from the fact that their last hard court meeting in Montreal this year went his way. If they do meet in the final, then it is likely to go all the way.