McEnroe wants to see a positive Murray
John McEnroe believes Andy Murray needs to be mentally stronger
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 when he was beaten in four sets by David Ferrer and he has now headed back home to London to begin practising on grass.
McEnroe said: "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."
He added: "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, 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."