Former British number one Annabel Croft believes Roger Federer will only retire when he stops enjoying the sport of tennis.
The Swiss ace has had a year to remember as he won his first Grand Slam since 2012 with his Australian Open win in January.
The 36-year-old continued to defy the odds as he followed it up with a record-breaking eighth Wimbledon win as well as a total of seven titles in 2017 so far.
The world number two is now currently playing in the ATP Finals in London as he looks to end a successful year on a high and Croft believes Federer's, as well as Rafael Nadal's success, has made it a mind-blowing year for tennis.
"It has been an absolutely mind-blowing year in tennis," Croft told Sky Sports News via Express. "I think nobody predicted when Andy Murray played Novak Djokovic in that final match at the O2 Arena last year that what would have happened this year."
"For Roger Federer and Rafael Nadal, nobody would have believed it. But it's happened, they've laid down the benchmark. Certainly for Roger Federer who is so fit and healthy and raring to go, he's the one to beat this year.
"He gets so much joy from the sport, he's so respectful of the sport and he's the most incredible ambassador as well."
There is also the concern that despite his astonishing year, age will continue to hinder Federer, who himself stated in October that he knew retirement was coming sooner or later.
However, Croft believes that rather than poor performances or a lack of honours, Federer will only retire if he stops enjoying the sport.
"I think as long as he keeps enjoying it, he's going to keep wanting to play and keep giving the crowds something to cheer about," she added.