LONDON -- Maria Sharapova has withdrawn from the season-ending WTA Championships because of an injured right shoulder.

The WTA says the third-ranked Russian will miss the Oct. 22-27 tournament in Istanbul because of the injury, which has sidelined her for most of the second half of the year.

Sharapova’s shoulder is said to be feeling a lot better lately, but she didn't feel like she had enough time to prepare for the event. She is scheduled to be back on the practice court in about two weeks.

As first reported by L’Equipe magazine, former French Tennis Federation fitness trainer Jerome Bianchi will join Sharapova’s team in November. Sharapova's longtime trainer, Juan Reque, decided earlier this year that he would exit after the season for family reasons.

Sharapova, who has been without a full-time coach since she ended her brief stint with Jimmy Connors in August, will name a new coach early next month.

Sharapova thanked Istanbul for being a "tremendous host" and said she hopes to play in Turkey in the future.

The WTA says Petra Kvitova of the Czech Republic, Sara Errani of Italy and Jelena Jankovic of Serbia have qualified for the championships. They join a field that already includes Serena Williams, Victoria Azarenka, Agnieszka Radwanska and Li Na.

The tournament features the top eight singles players and top four doubles teams.