ZHUHAI, China - Madison Keys has withdrawn from the semifinals of the Hengqin Life WTA Elite Trophy Zhuhai with an injury to her left knee.

"I am very sorry to have to withdraw from the tournament," the American said in a statement. "Zhuhai is such a wonderful city and I love playing in front of the fans here, so this was a very difficult decision. Thank you for all of support and see you all in 2019."

Keys had progressed from the Azalea Group with one straight-sets win against Daria Kasatkina and one three-set loss to Wang Qiang, but her left knee was visibly taped during her second match.

Keys will be replaced by alternate Wang, who will face Garbiñe Muguruza in the last match on Stadium Court on Saturday.