Former American pro John McEnroe believes that Andy Murray has the ability to win a Grand Slam but is worried that the Scotsman may not be able to handle the pressure.
The British number one has come close to clinching a major tournament, but fell at the semi-final stage in all four major competitions this year.
"You can't afford to waste energy, the game is so physical now," McEnroe told BBC Sport. "It's difficult to wrestle with the demons inside. I was someone who went through periods of negative energy which helped [my rivals] and hurt me.
"The fact [Murray] was knocking on the door all the time [in 2011] makes you more optimistic he'll finally get the breakthrough.
"But seeing the way he reacted [at big moments] made me worried whether he'd be able to handle it all the way through - to get through a Nadal and a Federer, a Nadal and a Djokovic, is obviously extremely difficult."
The tennis legend is currently competing in the AEGON Masters at the Royal Albert Hall in London.
