Federer failed to reach a grand slam final in 2013 for the first time in 11 years and saw his record run of 36 consecutive slam quarter-finals come to an end at Wimbledon.
Federer's total of 17 slam singles titles is three more than any other man but Rafael Nadal is only four behind and is five years younger.
Mark Philippoussis was the man Federer beat to win Wimbledon for the first time in 2003, and he believes the 32-year-old has one more grand slam in him.
The Australian said: "There's no way Roger Federer is finished. He's still a truly great player, perhaps the greatest, and he still moves really well.
"I think he has one more slam left in him but it will have to come next year or that will be it.
"I'm throwing it out there. It's a big call but I believe he can do it. Pete Sampras' last match was to beat Andre Agassi in the US Open final when everyone thought he was finished.
"I think Roger can either win in Australia or at Wimbledon next year. The fact that (Andy) Murray's fitness is a question mark is a factor and that improves Roger's chances as he lost to him in Australia last year."
Murray is recovering from a back operation but has begun his pre-season training in Miami.
Philippoussis is part of the field for the Statoil Masters Tennis at the Royal Albert Hall from December 4-8.
Philippoussis was drawn in a group with Tim Henman and Fabrice Santoro on Wednesday while Greg Rusedski, Pat Rafter and Goran Ivanisevic are in the other group.
That means there will be a repeat of the 2001 Wimbledon final, in which Ivanisevic beat Rafter in five sets to win his only grand slam title.