Brooks Koepka withdrew before the start of the third round of the CJ Cup because of a knee injury.

This fall the world No. 1 underwent a stem-cell treatment to repair a partially torn patella tendon in his left knee. On Wednesday, Koepka told reporters that his knee “feels good,” but he said in a statement released through the PGA Tour communications department that he reaggravated the injury when he slipped on wet concrete during a second-round 75 Friday in Korea.

Koepka was supposed to play in next week’s inaugural Zozo Championship in Japan, but now, after consulting with his doctor, he’s headed home to South Florida for further testing. He was the defending champion at the CJ Cup.

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Koepka never revealed his knee issue until earlier this month in Las Vegas. He said that his knee had been bothering him since March, and that it limited his practice sessions and caused him pain every time he leaned down to grab the ball out of the cup.

“Did my rehab, my recovery and there shouldn’t be any issues,” he said earlier this week. “There might be one more round of stem cells before the end of the year, during some off time. But other than that, I feel great. My knee feels good. It’s the first time it’s been feeling consistently good in a while.”

Koepka missed the cut at the Shriners Hospitals for Children Open and now faces an uncertain rest of the calendar year.