Roger Federer's former fitness trainer has made a big prediction on when he thinks the Swiss great will call it a day.
Paul Dorochenko was part of Federer's staff from 1998 to 2001 and played a big role in his development from a junior tearaway to the champion that he is today.
Dorochenko recently spoke about his time with Federer and what the World No.3 was like during training.
"In 1997, I was working with Sergi Bruguera and was called by the Head director of the Swiss federation who told me: 'We have a 17-year-old guy who plays well, I'd like that you become his fitness trainer'," he told Tennis World.
"I accepted and I was with him until he turned 20.
"Roger was a good guy, but he was heavy and wasn't focused. He threw racquets, so we can say he didn't behave well. But he was reading the ball very well, had an impressive forehand and was serving well."
Dorochenko said how Federer will go on for some time.
"I think two things allowed Federer to have a such long career: the first one is genetic, his body is doing well and has great muscles," he said.
"Then he has a good eye, he was training for it a lot. When he was younger he ate mostly pizza and hamburgers, but every kid does it. But he is professional, doesn't drink alcohol, doesn't smoke and travels with a fitness trainer.
"I think he's going to play until 40," he added.
"We already had Connors who played until 42 and Rosewall who reached the final of Wimbledon at 40. I see Federer doing the same, he takes great care."
Meanwhile, Federer has pulled out of the Cincinnati Open with a back injury, meaning Rafael Nadal will be the new world No.1 in next week's rankings.
Federer, who has participated in the Ohio warm-up tournament for the US Open on seven occasions, said he had picked up the injury in Montreal, where he lost to Germany's Alexander Zverev in the final.
Due to his age and wanting to stay in the best possible shape, Federer is now being extra careful when it comes to tournaments.
For example, he opted against competed in the French Open earlier this year in order to focus on Wimbledon, a decision that paid off as ran out victor at SW19.
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