Rafael Nadal (L) of Spain and Roger Federer (R) of Switzerland pat each other on the back before warming up for their men's singles quarterfinal match at the BNP Paribas Open ATP tennis tournament in Indian Wells, California, March 14, 2013.  [Photo/Agencies]

INDIAN WELLS, California - One of the most charismatic players in the game for nearly a decade, Rafa Nadal has commanded much more attention than usual at the BNP Paribas Open, his first hardcourt tournament in almost a year.

Though the Spaniard has made a highly successful comeback on clay in recent weeks, the hard courts of Indian Wells were always going to provide his toughest test on a surface where his all-action, fist-pumping style has been most vulnerable.

Following a shock second-round exit at Wimbledon last year, Nadal was sidelined for seven months by a left knee injury and the tennis world has closely monitored his recovery and progress ever since.

At Indian Wells, the 26-year-old world number five has so far progressed smoothly enough, winning two matches with one walkover in between to reach the quarter-finals of the elite ATP Masters 1000 event he has won twice before.

Nadal has shown no visible sign of discomfort, with his knee taped up throughout his matches and given extensive ice and phsyio treatment afterwards, but his fans and some of his peers are certainly worried about the prognosis going forward.

"It does concern me, especially what we have heard about his knee injury and how long he has been off," Ross Smith, a diesel mechanic from Vancouver who has become a regular visitor to the Indian Wells event, told Reuters.

"You kind of think, 'How long can this guy last playing this kind of tennis?' I don't think he's going to be able to keep it up personally. He's 26 and it's just that impact on his knee with all his rigorous tennis.

"It's just insane for these athletes to continue performing at that top level during a long tennis season, and especially the way that Rafa plays."

Physical Style

Serbian world number one Novak Djokovic, a long-time rival and good friend to Nadal, is well aware of the toll paid by the Spaniard because of his ultra-physical playing style.

"He really suffers on the hard courts," the Australian Open champion told Reuters. "I understand what he has to go through to play in such a style. He loves to slide.

"He loves to run around the court and do a lot of dynamic strong movements that eventually can hurt him, as they did in the last seven months.

"But being so long off the tour, I'm sure that he has taken his time and has been very patient. He has a smart team of people around him that advised him to take it easy, and now it has resulted with a great comeback."

It certainly made sense for Nadal to return to the circuit last month on his favourite clay surface and he flourished in South America, competing in three relatively minor claycourt events and winning two of them after reaching all three finals.

Perhaps no player understands better than Juan Martin Del Potro what Nadal is going through, the towering Argentine having missed eight months in 2010 due to wrist surgery.

While Del Potro has been hugely impressed by the smooth nature of the Spaniard's ATP comeback so far, he believes the mental aspect of Nadal's recovery will be crucial.

"It's very important to be strong mentally," 2009 U.S. Open champion Del Potro told Reuters. "For me, in the end, I was completely recovered from my wrist injury but in my mind it was still there and I couldn't play because when I hit some balls my mind is saying to me, 'You are still injured.'

"And then I would get an MRI or see the doctor and be told that my injury is gone. I don't have anything more in my wrist.

"But I think Rafa is working very well mentally, he is so strong as he shows in every match, so I think he is going to be much better than me with his recovery for sure."

No-Risk Strategy

Del Potro, who played just three tournaments in 2010 because of a lingering injury to his right wrist, said a no-risk strategy would be vital for Nadal to follow closely.

"He has really to be safe with his new problem, and on the hard courts here at Indian Wells that's a matter of how far he is going in this tournament," the 24-year-old from Tandil said.

"The big challenge for him is playing healthy, not feeling any pains and being ready to play tennis again.

"He has this tournament, maybe Miami and then the clay season comes again so he needs to be smart to play these tournaments, not put his knees at risk. If he is still feeling painful, it's going to be a tough moment for him for sure."

While Del Potro made a relatively quick comeback in terms of climbing back up the rankings, the 6ft-6in (1.98 metre) Argentine said it took him a year before he felt fully healthy.

"It took that long for me to be confident with my wrist and to get up every morning thinking about my tennis game and not about my wrist," he said. "It took all that whole year for me to be ready mentally again."

The crowd-pleasing Nadal, who has been given an electrifying welcome by vocal fans for his first two matches at Indian Wells, has relished the support but has repeatedly said that he does not expect too much too soon on the hardcourt surface.

"When you come back after seven months, you really understand how much you miss it, all of this," smiled the Spaniard, who missed last year's U.S. Open and January's Australian Open while on the sidelines.

"Two weeks ago I didn't know if I would be able to be here, so just being in the quarter-finals is a fantastic result for me. I need to keep doing. I need time and I need matches more on clay than hard."