Former world number one John McEnroe has issued words of warning for Andy Murray, stating that the Briton’s problems this year are no longer physical.
Murray has not made it to the final of an event on the ATP Tour since winning Wimbledon in 2013, and he has struggled to recover from back surgery that forced him to miss the end of that season.
But McEnroe, who won seven Grand Slam titles, believes that the 27-year-old is now beyond his injury problems, and that he is confused by his form this year.
No 'physical' blame
The former player, who won four US Open titles, is reported to have said: "It's difficult to say what's happening with Andy. It seems like the physical issues are behind him.
“It's impossible to say for sure from the outside but that's how it looks.”
Murray parted company witch coach Ivan Lendl in March, and he has made little progress on court since Frenchwoman Amelie Mauresmo took over the role in June, as he lost his Wimbledon title in July, losing in the quarter-finals to Grigor Dimitrov.
The Dunblane-born player has played in two tournaments since then, losing in the quarter-finals of the Toronto and Cincinnati Masters to Jo-Wilfried Tsonga of France and Switzerland’s Roger Federer respectively.
A big change
McEnroe feels the former world number two’s form has been hampered by his change in coach, a role he was linked with himself, and he is reserving judgement in the early stages of the pair working together.
“He made a big change - I thought he and Ivan worked well together," he added.
"To change course when he did is tricky so it remains to be seen what happens there.
“You need to give it more time to judge, but you sort of feel like the US Open would be a time he needs to step up because it's been a struggle compared to what it's been the last couple of years."
Murray will be seeded eighth for the US Open, which will be his lowest seeding at the tournament in New York since 2007, though he is still third favourite with some bookmakers, behind the top two seedings of Serbia’s Novak Djokovic and Federer.
The two-time Grand Slam winner will be looking to regain his title that he won in 2012, where he beat Djokovic in five sets to win his first major in his fifth final.
There is a chance that the British number one could face either of those players if he reaches the quarter-finals, and he has not been able to beat a player ranked inside the top 10 in 2014.
Despite some disappointing results in the last two Masters Series events for Djokovic, where he was knocked out in the third round of both, McEnroe still thinks the 2011 champion is the most likely player to win the last Grand Slam of the year.
"I think Novak had an incredible run at Wimbledon and it seems to me he is waiting for the Open," he concluded.
"I don't think it matters a whole lot what's happened with his results in the summer. To me, he's still the favourite going in.”
Federer has moved up to second seed after the withdrawal of Spaniard Rafael Nadal, who has been forced to pull out of the tournament with a wrist injury, and he will not be able to defend his title, which he won for the second time in 2013.