Former No. 1 Pete Sampras says Roger Federer could play for another "two, three, four more years" and add to his tally of 17 Grand Slam titles.

Speaking ahead of an exhibition match against Andre Agassi in London on March 3, Sampras said on a conference call that he is "amazed" by Federer's longevity.

Asked if Federer could win another Grand Slam title, Sampras says Wednesday "I think he can do it. That's why he's playing, I don't think he's playing for anything else but to win some more majors."

Sampras, who retired after winning his 14th Grand Slam title at the 2002 U.S. Open, said Federer should be comforted by his impressive run to the semifinals at the Australian Open.