Defending champion Brooks Koepka has withdrawn from the CJ Cup @ Nine Bridges, the lone PGA Tour stop in South Korea, after aggravating a knee injury.

The world No. 1 will not have a chance to win his second straight title in Jeju Island, after taking himself out of the no-cut event before the start of Saturday's third round. Koepka opened his title defense with rounds of 69-75 to sit in a three-way tie for 51st place at even par, 13 strokes behind the 36-hole leader Justin Thomas at the Club @ Nine Bridges.

Koepka underwent a stem cell treatment on his left knee during the offseason to repair a partially torn patellar tendon.

"During the course of Friday's round, I slipped on wet concrete, aggravating a previous injury to my left knee," Koepka said in a statement released by the PGA Tour. "After consulting with my doctor, I have been advised to withdraw from the CJ CUP and head home for further tests. I appreciate everyone's concerns and support. I'll keep you posted as I learn more."

Koepka had insisted all week his knee felt fine. During his pre-tournament press conference Wednesday, Koepka said: "Did my rehab, my recovery and there shouldn't be any issues. There might be one more round of stem cells before the end of the year. But other than that, my knee feels good. It's the first time it's been feeling consistently good in a while."

Then after his opening round of 69, Koepka said: "I can finally bend over and pick the ball out of the hole without hurting. That's always good."

Koepka, 29, missed the cut in his 2019-2020 season debut at the Shriners Hospitals for Children Open in Las Vegas earlier this month. (Yonhap)