American tennis legend John McEnroe believes that Andy Murray's back injury will hamper his chances at this summer's Wimbledon tournament.

The Scotsman has struggled in recent months with back problems and failed to retain his Queen's trophy after crashing out in the first round.

While the 25-year-old is ranked as the fourth best tennis player in the world, McEnroe believes that his status as a potential great is slipping.

"I had back issues and always wondered how mental or physical it was," said McEnroe. "A lot of stress goes to that part of the body and he's under a lot of stress. I remember watching Roger Federer play Wimbledon the first year he won it.

"He was struggling with his back problem. But somehow he dug a little deeper and won it. I'm sure everyone here is hoping that with Andy but this gap seems to be widening right now.

"He's bordering on great. But is he as great as [Novak] Djokovic, [Rafael] Nadal and Federer? That is a different issue."

Wimbledon gets underway next Monday.