Golf's World No.6 Bryson DeChambeau has tested positive for COVID-19 before his departure for the Tokyo Olympics and will be replaced in the United States men's team by Patrick Reed.
Reed joins Justin Thomas, Collin Morikawa and Xander Schauffele.
DeChambeau said in a statement issued by USA Golf: "I am deeply disappointed not to be able to compete in the Olympics for Team USA.
"Representing my country means the world to me and it is was a tremendous honor to make this team.
"I wish Team USA the best of luck next week in Tokyo. I will now focus on getting healthy, and I look forward to returning to competition once I am cleared to do so."
USA Golf executive director Andy Levinson added: "We're obviously disappointed for Bryson, as we know how much he was looking forward to representing the United States in his first Olympics.
"But we're thrilled that Patrick Reed is excited to play for his country when he is called upon, even with the strenuous testing protocols and he is set to arrive just in time to compete - on a golf course he will have never seen prior to the start of competition.
"It really illustrates the importance of the Olympics and the value Patrick places on playing for Team USA and for his country.
"We're excited to welcome him to Tokyo soon and know he'll be a formidable competitor for Team USA."
DeChambeau, 27, is ranked sixth in the world. He won the Arnold Palmer Invitational earlier this year for his eighth career PGA Tour victory. His only major title came at the 2020 US Open.
Reed, 30, prevailed at the 2018 Masters for his lone major championship. He has nine career PGA Tour wins, including the Farmers Insurance Open in January, and he is ranked 13th in the world.
Morikawa is ranked No. 3, Thomas is No. 4 and Schauffele is No. 5. Morikawa won the Open Championship last week for his second major title.