JEJU ISLAND, South Korea (AP) — Top-ranked Brooks Koepka withdrew from the PGA Tour’s CJ Cup before the third round Saturday after aggravating a left knee injury a day earlier when he slipped on wet concrete.

Playing his second event since stem cell treatment on the knee Aug. 25, Koepka shot a 3-over 75 on Friday at Nine Bridges after opening with a 69. The defending champion was 13 strokes behind leader Justin Thomas in the limited-field event with no cut.

“After consulting with my doctor, I have decided to withdraw from the CJ Cup and head home for further tests,” Koepka said in a statement. “I appreciate everyone’s concerns and support. I’ll keep you posted as I learn more.”

Koepka returned to Florida to meet with his doctors, leaving his status for the HSBC Champions in two weeks in China uncertain. He missed the cut two weeks ago in his season debut at Las Vegas.

The American won three PGA Tour titles last season, following his victory at Nine Bridges with wins in the PGA Championship and World Golf Championships-FedEx St. Jude Invitational. He has four major titles, also winning the PGA in 2018 and the U.S. Open in 2017 and 2018.