Moscow - Romania's world number one Simona Halep on Tuesday withdrew from the Kremlin Cup, a joint WTA and ATP event, due to concerns over an ongoing back injury.
"I tried everything I could to be ready here as I really wanted to play," Halep said.
"But unfortunately the back is still causing me pain and I don't want to take any unnecessary risks."
The 27-year-old's appearance in Moscow and the WTA Finals had been in doubt when she withdrew from Beijing two weeks ago and was diagnosed with a herniated disk in her back.
Halep, who has already qualified for the WTA year-ending finals in Singapore, said she needed more time to recover completely from her back injury.
"While it's disappointing to withdraw, I know it's important to put my health first," she added.
Halep this year played two Grand Slam finals, winning the French Open crown at Roland Garros, and won titles in Shenzhen and Montreal, leading the rankings for 40 weeks this year.