The French Open champion, 27, says she does not know how long she will be out but hopes to be back "soon".

The Romanian retired from Sunday's first-round match against Ons Jabeur at the China Open with a back injury.

"I will discuss with doctors in the next few days and will keep you updated," she said on Twittter.

The injury could force Halep to miss the end-of-season WTA Finals in Singapore, which run from 21 to 28 October.