Pete Sampras believes it would be foolish to write off Roger Federer's chances of winning an 18th major at the US Open despite the Swiss having just turned 34.

Federer's last Grand Slam crown came at Wimbledon in 2012, and his three-year drought is the worst of his career.

But Sampras, a 14-time Grand Slam title winner, insists the veteran can collect a sixth US Open to add to the five he won between 2004-2008 when the season's final major gets underway in New York on Aug 31.

"I think he's playing well, he's fit, he hits the ball great, he's doing everything that he's been doing for years ... I think he's capable of winning," Sampras told The Tennis Podcast when asked if Federer had a chance in New York.

But it won't be an easy road for Federer even if he still wouldn't be the oldest champion at the US Open.

That distinction belongs to Australia's Ken Rosewall, who was just two months short of his 36th birthday when he triumphed in 1970.

"It is tougher as you get older and now Novak (Djokovic) and (Andy) Murray, they're in their prime now," said Sampras.

"I think for Roger to win, things need to fall into place. I think if he has to play Murray, Djokovic, then Rafael Nadal in one week or back-to-back, it gets more difficult.

"Wimbledon I think is his best chance, but the US Open he's won there five times, he knows what he's doing. I think he's got a good shot, but I think obviously Novak is the man to beat."

Sampras had strong words for Nadal, the 2010 and 2013 US Open champion, who is currently enduring the worst slump of his career.

"I think he is still working hard. He is doing all the right things; he is just not playing as well," said the American legend of the Spanish star who saw his world ranking slip to a 10-year low after losing his French Open title in June.

"It just seems like anxiety is creeping in, he seems a little bit nervous, he's hitting a lot of short balls.

"Guys don't fear him as much and it's tough to play defense out there..

"When Rafa struggles, I think he feels like his career is over. But he'll be fine, he'll get back to where he once was."

(China Daily 08/18/2015 page23)