WUHAN (AFP) - World No. 1 Serena Williams announced Thursday her withdrawal from next week's China Open in Beijing and the WTA Finals in Singapore, ending her season.

"I am taking a proactive step and withdrawing from tournaments in Beijing and Singapore to properly address my health and take the time to heal," the 21-time Grand Slam winner said in a statement.

Williams has not played since she lost in the semi-finals of the US Open to Italy's Roberta Vinci, one of the most shocking upsets in tennis history.

"It's no secret I've played injured most of the year - whether it was my elbow, my knee, or, in the final moments after a certain match in Flushing (Meadows), my heart," Williams said.