Rafael Nadal said in an interview published on Tuesday that he has not picked up a racket since limping out of Wimbledon nearly three months ago and will only return to competition once he is fully fit.
"I'm not in any state to go on court at the moment. I haven't touched a racket but I am working hard every day," he was quoted as saying in an interview with four European newspapers, including French sports daily L'Equipe.
Nadal has been on the sidelines since his shock second-round exit at Wimbledon to unheralded Czech player Lukas Rosol in late June and has been receiving treatment for a torn tendon in his left knee.
The 26-year-old, whose injury has seen him miss the London Olympics, the Masters series events at Toronto and Cincinnati as well as the US Open, said he has been swimming every day to keep in shape and is also working out in the gym.
On September 5, Spanish tennis federation doctor Angel Ruiz-Cotorro ruled out surgery, raising hopes that he could make a return for Spain's Davis Cup final against the Czech Republic in November.
But Nadal appeared to pour cold water on a swift return when asked about when he would be next seen on court, telling reporters: "I don't know.
"The situation is very clear in my mind. I first need to look after myself completely and be back to full fitness before deciding when and where to play again. I'll only come back when I'm 100 percent.
"I don't want to go back on court again with permanent doubts on my fitness."
Nadal, the former world number one, has had repeated injury lay-offs in recent years because of knee trouble, which take much of the strain from his highly physical style of play.
The player said he was approaching his recovery calmly but admitted there had been "difficult moments", in particular missing the Olympics and the honour of carrying Spain's flag at the opening ceremony.
"I was very, very down for a couple of weeks. To miss a grand slam is hard but it doesn't come about every four years. I hope with all my heart to be at the Rio Games (in 2016). That's one of my goals," he added.