Brooks Koepka, who has been hampered by a knee problem for the better part of a year, withdrew from next week's U.S. Open at Winged Foot, tweeting, "I'm looking forward to getting healthy and competing at 100% again very soon."
Koepka has won two of the past three U.S. Opens and finished second to Gary Woodland last year at Pebble Beach.
Last month, Koepka was attempting to become the first player since Walter Hagen in the 1920s to win three straight PGA Championships, but he fell out of contention with a final-round 74 at Harding Park.
Koepka missed the cut the following week at the Wyndham Championship then withdrew from the first FedEx Cup playoff event, the Northern Trust, ending his 2019-20 season.
He has dropped to No. 8 in the world after beginning 2020 in the top spot. The four-time major champion had a stem cell procedure on his left knee after last year's Tour Championship then aggravated the injury at a tournament in South Korea in October. He didn't play again until January, and it's mostly been a struggle since.
Koepka finished seventh at the RBC Heritage after the PGA Tour's restart and tied for second in early August at the WGC-FedEx St. Jude Invitational. He was just two shots out of the lead heading into the final round of the PGA Championship before dropping to a tie for 29th.
"My golf swing's fine," Koepka said after missing the cut at the Wyndham. "If I can physically do it, then yes, everything's fine."
But Koepka has also complained about trying to get to his left side in his swing, and during the second round of the PGA Championship, he three times had a trainer help with his hip.
"It just locked up, cramped," Koepka said. "I couldn't do anything with it."
Paul Waring will replace Koepka based on his Official World Golf Ranking as of Aug. 23.
The U.S. Open begins Sept. 17 after being rescheduled from June due to the coronavirus pandemic.
