Moscow:World number one Serena Williams has blamed a knee injury for her decision to pull out of next week's 2.4 million dollar Kremlin Cup.
"I was experiencing knee problems since the US Open and now I need a break to regain my top form," the American star told organisers of the joint ATP and WTA event on Friday.
She added: "I played a lot of events this year and now I need a break to recover. My aim this year is to regain the world's top ranking. I played in the final here last year and will now lose a lot of points.
"But for now my only wish is to have some rest to recover and to be in my top form at Doha."
Jelena Jankovic of Serbia will replace Williams, a second round casualty at this week's Stuttgart WTA event, on top of the WTA rankings on Monday.