Venus WilliamsNo. 3 Venus Williams is done for the season because of a left knee injury that has sidelined her for most of the second half of 2010.

Williams has not played since the U.S. Open, where she lost in the semifinals to eventual champion Kim Clijsters.

She was to due to play in the China Open this week but withdrew because of her knee problems, raising doubts about her chances of playing in the Fed Cup final and the WTA Championships.

“I am very disappointed to announce that I will be unable to play in the season-ending WTA Championships and Fed Cup final,” she said in a statement.

“I have been getting treatment and therapy on my knee and have been making progress but unfortunately must continue to keep weight off my knee for the short term and won’t be ready to return to competition in 2010.”

Williams won 38 singles games this season, losing seven times and picking up two singles titles. She also won three doubles titles.