Nadal continues his quest for skills to unseat Federer

But appearances are deceptive. The 20-year-old Spaniard's high-octane mixture of aggression, athleticism and steely determination have helped make him the most entertaining player on the men's circuit.

The left-hander is the only player who has consistently managed to mount a challenge to Roger Federer's imperious domination of world tennis.

He has upset the Swiss six times in their eight meetings to date and is the only player to beat Federer more than once since he took over the number one spot in February 2004.

Nadal is the undisputed king of the clay court, extending his unbeaten record on his favoured surface to 60 matches as he claimed his second consecutive French Open in June with a four-set victory over Federer.

However, he is not the sort to rest on his laurels and the young Mallorcan is desperate to acquire the all-court skills that will give him a chance of one day unseating Federer as world number one.

Unlike many of his predecessors as Roland Garros champion, Nadal has also been keen to try his hand on grass and surprised many by making it all the way to this year's Wimbledon final, where he lost to Federer in an enthralling four-setter.

His enthusiasm to learn has earned him admiration from some of the game's most experienced players.

"It shows you the competitor's heart he has," Andre Agassi said during the grasscourt season. "Any time you got a ticker like that, you got to leave room for some great things."

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Four-times Wimbledon semi-finalist Tim Henman agreed with the American.

"When you compete as well as he does, it is dangerous to write him off on any type of surface," he said.

Together with Formula One world champion Fernando Alonso, Nadal is Spain's most popular individual sportsman, although his relaxed and down-to-earth demeanour make him a more accessible figure than the somewhat stilted Asturian.

Nadal first hit the headlines in December 2004 when he beat Andy Roddick to help Spain lift the Davis Cup at the age of just 18.

The following season he became the first man since Mats Wilander in 1982 to win the French Open on his debut, and victories in the Masters events in Montreal and Madrid helped him wrap up the season as world number two behind Federer.

His successful defence of the French title confirmed his status as the world's best on clay, but he surprised even himself by becoming the first Spaniard since Manuel Santana in 1966 to reach the Wimbledon final.

He will be out to provide further evidence that he is capable of becoming an all-terrain player when the U.S. Open begins on Monday.

Nadal lost to American James Blake in the third round at Flushing Meadows last year and has never progressed any further in the tournament, but the same was true of Wimbledon until 2006.

He is now less reticent to come to the net so he should be confident of giving a better account of himself this time round.

Defending champion Federer is, of course, the overwhelming favourite, but neutral observers are hoping the world's two best players pitted against each other in the final just as John McEnroe and Bjorn Borg were at the start of the 1980s.