Reigning Masters champion Hideki Matsuyama withdrew from the US PGA Rocket Mortgage Classic before Friday's second round after testing positive for Covid-19.
The 29-year-old world number 18 became the first Japanese man to win a major golf title when he captured the green jacket in April at Augusta National.
"It's disappointing to receive this news and have to withdraw from the Rocket Mortgage Classic," Matsuyama said in a statement released by the tour.
"I will take all the necessary precautions to ensure the health and safety of all others. I appreciate and thank everyone for their concern in advance. I look forward to a full recovery and returning to competition as soon as possible."
Matsuyama opened with a level par 70 in the first round at Detroit Golf Club.
His departure forced six-time major winner Phil Mickelson and fellow American Rickie Fowler to play in a twosome on Friday.
Matsuyama is set to represent Japan in the Olympic golf tournament from July 29-August 1 and is entered in the British Open on July 15-18 at England's Royal St. George's.
Under Covid-19 protocols, Matsuyama must quarantine for 10 days or until he returns two negative tests more than 24 hours apart.