MADRID - Spanish tennis ace Rafael Nadal this Tuesday spoke about his battle to retain full fitness after suffering a knee injury in June.

The 26-year-old has not played a competitive match since his shock second round defeat in Wimbledon.

Speaking to Spanish sports paper, Diario AS, Nadal was honest about the extent of the problems he has suffered in his left knee, which this year have been more serious than ever and which caused him to miss the Olympic Games, where he was to have been the flag-bearer for the Spanish team, as well as the US Open and other major tournaments.

Spanish tennis player Rafa Nadal poses with playing cards depicting some of his 11 Grand Slam victories after an interview with Reuters in Madrid, Sept 18, 2012. Rafa Nadal's steady recuperation from a knee injury is proceeding according to plan and he is not going to rush back before it has healed properly, the world number four said. [Photo/Agencies]

"I am working very hard, although I am doing nothing on a tennis court," explained Nadal.

"I am undergoing swimming and rehabilitation sessions, working in the gym and with my physiotherapist. I am doing weights, bicycle and working to get to the condition I was in before suffering the injury."

"I swim a kilometer every day, the knee is responding well, but my only aim is to return when it is 100 percent cured. The only reality about my options of returning in 2013 is, that I still don't know," he said, regretting the moment he had been affected, shortly after winning an incredible seventh title at Roland Garros.

"I was playing some incredible tennis," he commented. "It was one of the best Roland Garros of my career, but it was there that the pain started. I needed to take anti-inflammatory drugs before the semifinal and the final," he explained.

Nadal kept on until Wimbledon, where he lost in the second round, but with hindsight, he now believes he probably should not have competed in London.

"There is a moment when your knees tell you that you have to stop, when the pain starts to limit you. When you get to that point, then it is impossible to compete," he admitted.

The Spaniard already has an incredible list of successes with seven French Open titles, two titles at Wimbledon and US and Australian Open titles, as well as a host of Masters Series events. But despite his success and the problems caused by his injury, he has no intention of giving up his battle for fitness and retiring.

"I have sufficient motivation to carry on trying. This injury has not forced anyone to retire," insisted Nadal.