World number one Serena Williams has opted to pull out of the WTA Finals and end her season early following a roller coaster campaign that has taken its toll on her body, the American said on Thursday.

Williams, 34, has not played since her shock loss to Italy's Roberta Vinci in the semi-finals of the US Open last month, which ended her bid to claim all four grand slam titles in the same season.

The 21-times Grand Slam singles champion said she had been carrying injuries and the loss to Vinci had taken its toll, adding she would not play again this year after also pulling out of next week’s China Open.

“My journey in tennis this year has been at times exhilarating, at times disappointing,” Williams said in a statement carried by China Open organisers.

“I’ve played injured most of the year - whether it was my elbow, my knee, or in the finals moments after a certain match in Flushing, my heart.

“I’m a fierce competitor and I want to compete as well as I can, for as long as I can.

“This is a very difficult decision, but one ultimately made because of the love of the game.”