THE knees may creak a little, the face has lost its youthful chubbiness, but the essence of Rafael Nadal is unchanged.

"When I lose is because I don't have more," he said yesterday. The English is fractured, but the will is unbroken over a stellar career in tennis.

He was answering a question about motivation. It remains unchanged for Nadal despite the successes, despite the debilitating injuries. He just plays to win. He loses because sometimes, even for a player of Nadal's talent, giving everything is not enough.

His simplicity of purpose is complemented by an extraordinary personality. The Spaniard is belligerent, almost pugilistic, on court but there is grace in his words.

Nadal comes to Wimbledon with an eighth French Open title in his bag. He is a genuine great. He is genuinely humble.

His defeat by Lukas Rosol last year in SW19 ended his season as the knees finally buckled. Yet Nadal has returned this year to play nine tournaments, and reach nine finals.

With world No.1 Novak Djokovic, he is the greatest threat to Andy Murray's hopes of winning a Wimbledon title.

There is no doubt that Nadal faces a particular challenge at Wimbledon 2013. He is coming back from a long-term injury to a surface on which he has not played competitively for a year. He may also have to defeat Roger Federer, Murray and Djokovic to win a third Wimbledon title.

The 27-year-old admitted that he envisioned this season as a "transition" year after surgery on his knees. His blistering form means that assessment has had to be revised. "Last year I played here because is a tournament that I love, but I was not ready to play here," he said.

With the hardcourt season beckoning, and the knees possibly quaking at the prospect of playing on such an unforgiving surface, Nadal would not commit to outlining a schedule for the rest of the year.

He remains focused on the challenge of SW19 and is philosophical about the problem his fifth seeding gives him in the more difficult half of the draw. "I don't see them before quarter-finals and semi-finals," said the Spaniard of potential matches against Federer and Murray. "So I have a long way to work before that."

He added: "My view is if I arrive to quarter-finals is because I will be ready. Then you can win, you can lose. But for me, going to be very tough to be there. I gonna try."

The last was the most unnecessary sentence of this or any other Wimbledon. Nadal's effort will be relentless and he would relish the chance of facing Djokovic in the final.

The Serb properly remains the favourite for the tournament as he is simply and consistently the best player in the world. Yet he arrives at Wimbledon seeking to impose his preeminence. Djokovic's superb form in 2011, winning three Grand Slam tournaments, was taken as a sign of a dominance that would be paid out in majors. Yet Federer, Murray and Nadal have all won Grand Slam titles since that marvellous year for the Serb.

It would be absurd to suggest that Djokovic's star has waned but his desire to win at Wimbledon is both prompted by the need to reassert himself and to assuage the wound of Roland Garros where he could have beaten Nadal in a spectacular semi-final.

When discussing the stress of Wimbledon, Djokovic referred to how Murray reacted to the tournament's hype.

"I guess that adds a little bit of extra pressure to him because he has got huge expectations from his country because they have been waiting for the local winner for many years," he said.

"But he's got much better since last year this time because he has played finals at Wimbledon. He came back and won an [Olympic] gold medal. He won the US Open. He's got already a few big titles under his belt, and he knows definitely what it takes to play on a big stage. I think he handles pressure really well."

He added: "But everybody feels pressure. Pressure is part of what we do, part of professional sport. It's a challenge, but it's also a privilege because having pressure means that you're doing something that is important, that is very valuable. You have to learn how to deal with it and accept it."

It could be stated, however, that the big pressure is on Djokovic, who is a short-priced favourite but has lost two of his last three Grand Slam finals. Nadal, after all, has surpassed all personal expectations in coming back from injury to win a major. Federer has been dismissed, perhaps prematurely, as someone with his best days in the rear-view mirror. Murray has spoken convincingly of feeling much more relaxed since finally win that major in Flushing Meadows.

Djokovic may just feel it is time he flexed his muscles again. He remains the most persuasive answer to the beguiling question of who out of the Big Four will win the big one.