Lleyton Hewitt backed Roger Federer to extend his career for a little longer yet after his run to the Wimbledon semi-finals.
The Swiss great's wait for an 18th grand-slam title continues after his five-set loss to Milos Raonic in the last four at the All England Club.
Federer, 34, is without a major crown since 2012, but has reached the semi-finals at two slams this year.
Hewitt, the Australian two-time grand-slam champion, said Federer still looked like he was enjoying the sport.
"He's so competitive and he wants to get out there and push himself as hard as he possibly can," he told Omnisport.
"And when you do retire you retire for an awfully long time so I think he's still enjoying being out there.
"He's played through generations as well which is impressive and now playing against the likes of [Novak] Djokovic, [Andy] Murray and some of the younger guys that are at the top of their games, I think he's enjoying pushing himself to that next level."
Federer has battled injuries this year, undergoing surgery for the first time in his professional career in February due to a knee problem.
Hewitt said Federer's run at Wimbledon was proof he was still capable of taking on the world's best.
"He's been around the top, he's been the top dog for so many years and every single match he goes out to play, all the lower-ranked underdogs are wanting to knock him off and you really do have to take your hat off to him," he said.
"He has kept his body in great shape. He is moving as well as he has ever moved. He's had a couple of niggling injuries I guess over the last six to eight months, which has made it slightly harder.
"But when he gets on the grass court at Wimbledon he can still compete against the very best players."
Hewitt was speaking on behalf of HSBC, the Official Banking Partner of The Championships, who are committed to supporting tennis from the back garden to Centre Court.