John McEnroe says he expects the rivalry between Roger Federer and Rafael Nadal to last at least a few more years before a new face breaks through the top ranks of men's tennis.

The two players have swept nearly all the Grand Slams and controlled the top two spots in the rankings in recent years. Both players have won all four majors, with Nadal completing his trophy collection by winning the U.S. Open for the first time in September — his third consecutive Grand Slam title after wins at the French Open and Wimbledon.

"There's no reason to believe ... that these guys aren't going to be around for the next couple of years," retired American tennis great McEnroe said Tuesday on the sideline of an exhibition tournament in Hong Kong.

While Nadal dominated last season to seize the No. 1 ranking from his 29-year-old Swiss rival, McEnroe said Federer was still enthusiastic about the game and finished the season on a high note. The 16-time Grand Slam champion beat Nadal — five years his junior — to clinch the season-ending ATP World Tour Finals in London.

"He still seems to love to play. He's finished the year very strong," said McEnroe, a seven-time Grand Slam champion.

"We have an incredible rivalry that hopefully will last another couple of years, a year or two more, and we can take advantage of that," he said.

McEnroe said world No. 3 Novak Djokovic and No. 4 Andy Murray still need to improve to break the Federer-Nadal stranglehold.

"They're going to have to add elements to their games ... and to work harder than ever to try to allow themselves to compete against two of the most — if not the most — talented players that ever played tennis," McEnroe said.

As they step up their preparations for the first major of the year, the Australian Open, Federer and Nadal faced off in the final of the Abu Dhabi men's exhibition tournament last week, where the Spaniard prevailed in two tight sets that had to be decided in tiebreakers. Both are competing in the ATP tournament in Doha this week.

The European domination at the top has translated into an extended drought for the American men. While the U.S. boasted major champions like Pete Sampras, Andre Agassi, Jim Courier and Michael Chang in the 1990s, the Americans have faded in the new millennium.

The last American man to win a Grand Slam was Andy Roddick, who claimed the 2003 U.S. Open. Roddick is currently the only American in the top 10 at No. 8. There are three others in the top 20: Mardy Fish at No. 16, Sam Querrey at No. 18 and John Isner at No. 19.

Roddick, 28, and Fish, 29, however, are reaching the end of their careers.

McEnroe said Roddick may have a few good years left in him, but he wasn't bullish about the major prospects of the younger Americans.

"At the moment, I see Isner and Querrey as excellent players bordering on great players, but I don't see them breaking and winning majors," he said, although adding that both "made some excellent strides in their careers" and deeming them both top 10 material.

As for another much-touted junior, Ryan Harrison, McEnroe said he still reserves judgment. The 18-year-old is just starting his senior career and is currently ranked No. 173.

"He's certainly a very capable player who could go a long way. I can't say that I think he's going to turn around and win a major right now. I'd like to see him (do that) — hopefully if he makes the type of improvement he has the last year," he said.

For his part, McEnroe said he is scouring for talent through his tennis academy in New York City.

"It's very important for us and the popularity of the game to have an American challenging and winning at Grand Slams."