Rafael Nadal has withdrawn from the ATP Tour Finals with a long-standing knee injury.

The Spaniard was ruled out for two months at the start of September with a torn knee tendon which had prevented him from defending of his Olympic title, the US Open and the Davis Cup semi-final.

And having not hit a ball in anger since his third round exit at the hands of Lukas Rosol at Wimbledon, Nadal has pulled out of the season ending finals in London, as well as the Paris Masters.

Rafael Nadal
Nadal is expected to return at the Australian Open.

"It's disappointing for me to miss the last two tournaments of the season in Paris and London, but it doesn't come as a surprise," Nadal said.

"I will hopefully resume my tennis practice soon since I am making good progress with my recovery from injury. I am not ready to compete in time for these events so I will continue my recovery in Mallorca and work hard to be back as soon as possible."

ATP Executive Chairman Brad Drewett said: "We wish Rafa all the best as he continues his rehabilitation from injury.

"Rafa is an incredible champion and it goes without saying that he has been missed on the ATP World Tour over the past few months. We look forward to welcoming him back on the tour very soon."

Upon learning the news of his two-month absence in September, the 11-time major champion hinted towards a possible return at the Australian Open next year, with the announcement over his absence from the year's final two events all-but ending his 2012 campaign.

Nadal has committed to playing in the year ending exhibition event at the three-day Mubadala World Tennis Championship in Abu Dhabi, alongside Novak Djokovic and Andy Murray, but despite having claimed the current knee problem causes him no pain, an extended period of rest is more likely.

Such is the severity of Nadal's left knee injury that it is expected to dictate his participation in the first half of the American hard-court season, with the surface having contributed to his current problem.

The withdrawal means three more qualifying spots for the finals at the O2 Arena are now available and are currently occupied by Juan Martin del Potro, Jo-Wilfried Tsonga and Janko Tipsarevic ahead of the final qualifying tournament in Paris.