After a shock quarter-final loss to David Ferrer in the Australian Open, World No. 1 Rafael Nadal revealed that he was still uncertain about the injury that had deprived him from playing at his highest level.

When asked about the injury, he said, I can say nothing about the injury. Seriously, I would prefer not to talk about it. For respect to the winner and a friend, I'd prefer to talk about the match.

Nadal, who had to get his left thigh strapped in the first set, ended up losing 6-4 6-2 6-3 to Ferrer who will go on to meet Britain's Andy Murray in the semi finals.

The 24-year-old was understandably disappointed after missing out on the opportunity to hold all four grand slams.

It is a difficult day for me but I tried my best and couldn't do any more. In tennis you have highs and lows. In my career I have had almost always good moments. Last year I was very lucky, I was healthy for most of the year. This year I have done everything to start the season well. I played well in Abu Dhabi but after that the problems started.

This is one of the negative moments. That's part of the sport. If I am ready to accept both things the same then I will be able to come back and play my best tennis another time. I love playing tennis and love the competition.

When he queried again on the injury he said, It's obvious that I didn't feel my best and had a problem during the match, at the very beginning. After that the match was almost over. It's difficult to come here and speak about it. In Doha I wasn't healthy and today I have another problem.

It seems like I always have a problem when I lose and I don't want to have that image. I can't tell you what problem I have because I don't know. I don't have to tell you about what I felt on the court because I tried my best all the time.

Despite the loss to his close friend Ferrer, Nadal said he would love it if his fellow Spaniard was to go on and win the tournament.

He's playing fantastic. But I think he's not the favorite. But if he keep playing like this, hopefully he can have a good chance to be in the final or win the tournament. I would love that.

David is a fantastic person and is a close friend of mine so I wish him all the best. I think that Andy (Murray) is playing very good, too, but David is playing at high level, no? If he's able to keep playing like this, I think he is going have a good chance.