Maria Sharapova on Monday withdrew from the season-ending WTA Championships in Istanbul because of a right shoulder injury that has dogged her since before the US Open, The Women's Tennis Association announced.

The 26-year-old Russian - currently No 3 in the world - had had to withdraw from the US Open on the eve of the tournament because of the injury and, owing to a previous hip problem, she has played just one match since a second-round exit at Wimbledon in June.

"I am very disappointed that I will not be able to play in the WTA Championships this year," said Sharapova, whose turbulent season has also been marked by her splitting with Jimmy Connors after just three weeks as her coach.