The 37-year-old Sampras, who is in London to play in a seniors tournament at the Royal Albert Hall, won the 2002 U.S. Open in his last competitive match, giving him 14 Grand Slam championships. Federer has 13 and Nadal has five, including the last four French Open titles.
"If you think about it, Rafa's got as good a chance to win double digits as anyone,'' Sampras said Tuesday. "I think Roger's going to break this record over the next couple of years. I think Rafa, he could win some more French's, he could win a couple more Wimbledons. He could have 10-12 majors when he's done, if not more.''
The 2008 season saw a shift on the tennis circuit from Federer's dominance to the ultimate rise of Nadal, who beat the former top-ranked Swiss to win both the French Open and Wimbledon and took over the No. 1 ranking.
This year's Wimbledon final was considered one of the greatest matches of all time, with Nadal winning 9-7 in the fifth set in near darkness.
"One guy had to win. It was Rafa's year,'' said Sampras, who won seven titles at the All England Club. "It was one of the best matches I've ever seen.''
But even though Nadal got the upper hand this past season - finally beating Federer on grass to snap his five-year winning streak at Wimbledon - Sampras believes Federer has plenty more titles to win.
"There's a lot left in him,'' Sampras said of Federer, whom he called a friend, adding they text each other regularly. "I think he's gotten to a stage where it's about the majors.''
As for next season, Sampras is already curious.
"It'll be interesting to see what happens with Nadal next year,'' Sampras said. "It takes so much work for him to keep it going, to stay healthy, to stay on top. That's one thing Roger has over him. I think it takes a lot less energy for Roger to stay on top.''
Sampras also talked about Andy Murray and Novak Djokovic, saying both are just a step below the top two players but a step above everyone else.
"He's right there with Nadal and Roger,'' Sampras said of the fourth-ranked Murray, adding that he hasn't been asked to give any advice to the British player. "I do know what it takes to win Wimbledon, if he wants advice on that.''
This week's BlackRock Masters tournament marks the first time Sampras has been to Britain since 2002, when he lost to George Bastl in five sets in the second round at Wimbledon.
"Last time I was here was a major low point, but I feel pretty good. At 37 I can still play pretty well,'' said Sampras, who won a seniors event in June in Brazil. "I can still serve and volley really well.''
If they would let him, Sampras would even put on his whites this week for another chance to get on the court at the All England Club - if only for practice.
"I've missed the place,'' said Sampras, who won three straight Wimbledon titles from 1993-95 before winning another four straight from 1997-2000. "I'd like to play on the court one more time. Take my kids there.
"There's no other place like it in the world.''
This week, Sampras will play John McEnroe, Jeremy Bates and Cedric Pioline in Group A of round robin play, starting with McEnroe on Wednesday. Greg Rusedski, Pat Cash and Guy Forget are in Group B.
"It's still competitive. We all have a lot of pride in playing well and winning,'' Sampras said of the seniors tour, before noting it's not exactly the same as when he was at his peak. "It's not like I need to come here and have to win the event. I mean I'd like to, but it's not like it used to be.
"That being said, people want to see me play well. And all the guys play well.''
He'll try to play better than he did in his last appearance in Britain, even if certain things rarely change.
"It's raining still,'' Sampras said with a smile as drizzle fell outside the Royal Albert Hall.
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