Rafael Nadal's participation in the remainder of the tennis calendar is in major doubt with the Spaniard's troublesome left knee causing him to miss another two months.

The 26 year old, who pulled out of the Olympics and the US Open due to the injury, has withdrawn his availability for this month's Davis Cup semi-finals, and will miss both the Shanghai and Paris Masters in October.

Having not played since defeat to Lukas Rosol in the second-round at Wimbledon, a further two month absence throws into doubt Nadal's participation in the season ending ATP World Tour Finals in London, an event the world No.4 has never won.

Rafael Nadal
Nadal could miss the rest of the year with a knee injury.

"Rafael Nadal will not play in the next 2 months and will stop to rest and recover his knee," a statement read. "Among other things he won´t be able to be at the disposal of the Spanish Davis Cup captain for the semi-finals tie against the USA.

"Rafa has partial tear of the patella tendon at the distal pole of the patella plus an inflammation of the Hoffa's fat pad of his left knee.

"Since the diagnosis of that tear, Rafa has been receiving medical treatment consisting on specific medication, physical therapy and a progressive program of rehabilitation and muscular potentiation."

The problem is the latest in a catalogue of knee issues for Nadal, an injury which has dogged his career ever since he burst on the scene in 2005, becoming the first teenager to win a grand slam title since Pete Sampras, in claiming the French Open.

Nadal pulled out of the Davis Cup final against Argentina in 2008 and of Wimbledon in 2009, when returning as defending champion, due to tendinitis in his knee and has regularly cited the gruelling hard court tournament schedule on the ATP tour, which takes significant toll on his body, for the reason behind his wavering physical condition.

The tentative two-month recovery period means Nadal is likely to miss the remainder of the tennis calendar, with the season ending ATP Tour finals beginning on 5 November; an event should the 11-time grand slam champion wish to participate would be his first tournament in over four months.

Rafael Nadal
Knee injuries have dogged Nadal's career.

"I have missed the Olympics and the US Open in the last few weeks, two of the most important tournaments of the year and that I really wanted to play," Nadal says.

"I really want to be back competing and enjoying the tennis tour, but I have many years in front of me and my knee needs some rest. I will be back when I have no pain and able to compete with guarantee.

"I feel better after the meeting with my doctors and happy knowing that the evolution of the past weeks has been positive and surgery has been avoided.

"I will continue to work with the plan my doctors have established to be able to compete as soon as possible in the right conditions.

"I would also like to thanks all for the support I am receiving these days."