Rafael Nadal, Roger Federer
Rafael Nadal of Spain and Roger Federer of Switzerland hug at the net, after Nadal won their men's singles semi-final match at the Australian Open 2014 tennis tournament in Melbourne Reuters

American tennis great Pete Sampras said former world's no.1 Roger Federer can still play high-level tennis for at least four more years, adding the Swiss Master could add another Grand Slam to his 17-majors championship.

Sampras, who is scheduled to play an exhibition tennis match with fellow Hall of Famer Andre Agassi in London, admitted that he's amazed by Federer's love for the game, withstanding the rigors of being a professional tennis player.

"He's got a true love of the sport, doesn't mind the travel, doesn't mind the lifestyle. He seems to enjoy it. I'm amazed he finds the motivation to play the outside events, although obviously the majors are his main motivation. I found myself getting tired when I hit about 30, 31 - he's still enjoying it.He could play another three or four years," Sampras told the Guardian.

Sampras added that Federer's fire of competitiveness remains brimming, and that would be enough for him to stay in the sport as he attempt to win another Grand Slam or two before he closes out his epic tennis career.

"If Roger feels that he can't compete at the highest level, I don't see him playing just to play. He'll play for the majors and maybe to be No 1."

"Those days could be over, and I'm not sure he has to do it or wants to do it. I think if he can't win majors and can't be competitive, then he'll step aside. But I don't see that happening. I think he'll be competitive, still be involved in the mix. We'll see how the year unfolds. But things do get tougher as you get older, to keep up the pace, and he's been out there a few years. He's a special player, and he'll be able to figure it out," said Sampras, who boasts 14 Grand Slam championships around his belt.

Still, Sampras believed Federer's main priority right now is not to climb atop the ranking but to become a force again in majors championship, including the Wimbledon Open where the Swiss has a chance to book a record-setting eight titles at All England Club.

"He struggled a little bit at times, although Rafa's just a rock. But I do see Roger building from that. I think he's going to have a good year. Obviously the French and Wimbledon are his next main goals, and I do think he can win another major. Everything needs to fall into place and he needs to play well, but 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, and Wimbledon is the most likely," Sampras added.