Monaco, 9 April 2011 | AAP

Novak Djokovic has pulled out from the Monte Carlo Masters because of a knee injury.

The second-ranked Djokovic, a finalist in 2009, said in a statement that his withdrawal is a “tough blow” because the Monte Carlo Masters is “his favourite tournament.”

Djokovic was set to start his clay-court season at Monaco next week. He didn’t say how long he will be sidelined.

The Australian Open champion has had a stunning start to the season and is 24-0 in 2011.

Djokovic has won 59 of 65 sets and four tournament titles on three continents.