John McEnroe has told Andy Murray to forget about his back problems and present a more positive image to opponents if he wants to break his grand slam duck.
The world number four's French Open campaign came to an end in the quarter-finals on Wednesday when he was beaten in four sets by David Ferrer and he has now headed back home to London to begin practising on grass.
It was another eventful fortnight for Murray, who came into the tournament with a nagging back problem, almost went out in the second round when his back went into spasm before battling his way into the last eight.
The Scot was at his best in the fourth round against home favourite Richard Gasquet as he revelled in the crowd's boos, but he again cut a frustrated figure against Ferrer, frequently clutching at his back after losing points.
McEnroe has been critical of Murray in the past for being too negative on court and shouting at his support team, something the 25-year-old has tried to address - particularly since appointing Ivan Lendl as coach at the end of last year.
Murray appeared to have made a leap forward when he pushed Novak Djokovic all the way in an epic Australian Open semi-final in January, but since then the top three of Djokovic, Rafael Nadal and Roger Federer have pulled away again.
McEnroe said: "He's got an interesting dilemma, because with Lendl, I'm sure he didn't get hired to get berated like the other coaches were.
"So he doesn't quite know how to answer this, I'm guessing, because he used to seemingly fire coaches while the match was going on.
"He's figuring out a way how to handle this. He's worked exceptionally hard but, as unbelievable amount of effort as I have heard he's put in in a lot of ways, it hasn't really paid off in the way people expected.
"So that's got to be frustrating. If anything, people are saying the gap is getting bigger, not smaller. So time is becoming of the essence.
"It almost seems like he's just got to get that mental part of it where he's got to forget about it. 'I don't care if my back is hurt, I'm not going to show it.'
"It can work against some guys, I guess, but it's not going to work against the best guys. That's what he's got to think about if he's going to win slams. These is guys are tough to beat, really tough."
Murray revealed recently he has been battling an ongoing back problem since December, although he has so far refused to give any more details.
At a press conference on Thursday, McEnroe talked about his own back issues, saying: "I had matches in tournaments at times where I would have sworn I had a back problem.
"Suddenly I'd feel like I can't even play, I can't get out there, and then I'd go out and somehow the adrenaline would kick in and all of a sudden you'd be like, 'Wait a minute, do I have a back problem?' You're second guessing yourself."
Murray was happy to admit he had lost to the better clay-court player in Ferrer, and he felt he had got his tactics and approach right despite making 59 unforced errors.
The Scot said: "I feel like I went for my shots. If I hadn't done, I would have got criticised for that. If I do go for my shots, then I get criticised for making mistakes.
"I played the way that I thought was best to win the match. I don't think it was down to a psychological thing because I went for it, and it was just down to poor execution of the shots."
Murray is scheduled to play in the AEGON Championships at Queen's Club next week, where he is the defending champion, and, although he did not commit 100 per cent to doing so, it is understood he is not planning to pull out.
The 25-year-old said of his physical state: "I feel okay. I'll need to put some good work in before Wimbledon, that's for sure. I was getting a little bit out of breath after some of the longer rallies."
Murray is also hopeful playing on grass will be kinder to his back than the gruelling rallies that are such a feature of clay-court tennis.
He said: "We'll see how it feels over the next few months. But I'm sure I'll have to answer it many times over the next few months.
"Every player has niggles. Everybody has problems from time to time. Everyone has to find ways of dealing with them.
"I think the grass will probably help a bit. You're not having to generate as much power because the ball is coming into you a little bit more and doesn't get up as high as it does on the clay."