Rafael Nadal has a partially torn patella tendon in his left knee and will be sidelined for at least the next two months, including Spain's upcoming Davis Cup semifinal against the United States.

In a website posting linked on his Twitter feed, the 11-time Grand Slam champion says he "will be back when I have no pain."

He adds: "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."

Nadal has been out of action since losing in the second round of Wimbledon in late June, missing the London Olympics and the U.S. Open.

The season-ending ATP World Tour finals begin in London on Nov. 5.