Andy Murray has hailed Roger Federer's longevity ahead of their Wimbledon semi-final clash on Friday.
British number one Murray admitted that the evergreen Federer shows no signs of slowing down, despite the prospect of the Swiss turning 34 next month.
The Scot told reporters: "I have no idea how long he can keep competing at the top level. No one knows. It could be three, four years at the rate he's going just now, if he wants to continue or not.
"The reasons he's still at the top is he has a pretty efficient game style and he's quite loose on the court. It's very impressive that he's managed to stay at the top of the game for so long, considering how long he's been at the top and how many matches he's played.
"He's won over a thousand matches and played over 1,200 matches. That's a lot of tennis."