Golfer Vijay Singh has pulled out of the Chevron World Challenge tournament.

Singh had surgery on his knee and will not be able to defend his title. He has been recovering well but it may take time before he starts to play again.

Singh is hoping to be back as early as next year. He has been replaced by American Justin Leonard for the event, which raises money for Tiger Woods's charitable foundation.

The Chevron World Challenge golf tournament will be held this weekend.