Wimbledon 2015: Stamina will be Roger Federer's downfall, says John McEnroe
Roger Federer is in scintillating form ahead of his semi-final against Andy Murray but may not have the stamina to seal a record eighth Wimbledon title, says three-time champion John McEnroe.
Federer has dropped only one set en route to his last-four clash with the British number one and is now just two victories away from an 18th grand slam triumph.
The Swiss has enjoyed a kind draw at the All England Club but a number of superb displays suggest he is capable of securing his first major title since beating Murray to win Wimbledon in 2012.
A back injury looked to be pushing Federer into decline in 2013 but the world number two has enjoyed a renaissance since appointing Stefan Edberg to his coaching team 19 months ago.
Federer has won his last three meetings with Murray, including a 6-0 6-1 demolition of the Scot in November, and McEnroe admits the Swiss has shown championship-winning form over the past 10 days.
"I didn't think Roger was going to win another one," McEnroe said. "But every time I watch him play like this, you've got to think, 'Well, of course he's got a chance if you're playing this well'.
"But to beat Murray, and in all likelihood Djokovic, to do that back-to-back, best-of-five, that's a tough situation for Roger.
"So that's why I've picked Murray to win the tournament but it's going to be an incredible match."
Federer has come out on top in 12 of his 23 career meetings with Murray but their last match-up on grass remains the Scot's Olympic triumph in 2012.
The seven-time champion has beaten Gilles Simon, Roberto Bautista Agut and Sam Groth to reach the semi-finals and against Simon won his 116th consecutive service game to break a record set by Wayne Arthurs in 1999.
"Roger Federer is playing so unbelievably well - this guy can make it look so easy," McEnroe said.
"In the fourth round, he made (Roberto) Bautista Agut look like he was number 1,000 in the world, and the guy's 20 (he is 22) in the world.
"He made him look like a guy in the juniors back there so he's at a level that you've just got to take your hat off to the guy."
No player has won more men's titles at Wimbledon than Federer, who currently sits top of the open era list along with fellow seven-time champion Pete Sampras.
An eighth success at SW19 would surely cement the Swiss' place as the greatest grass-court player of all time but Murray's coach Jonas Bjorkman believes the Swiss has nothing left to prove.
"I don't think he needs to win the eighth to be considered the best here," Bjorkman said.
"Sometimes there is so much speculation about records but winning seven is pretty good."
Federer turns 34 next month and Murray said after his quarter-final victory that his next opponent could enjoy another "three or four years" at the top.
"The way he's prolonged his career is incredibly impressive," Bjorkman said.
"He has a very natural game, he is not expending a lot of energy in his game and with a good body like he has, that is how he still manages to play phenomenal tennis year in year out. You can never count him out."