World No.16 Tony Finau has been withdrawn from the Shriners Hospitals for Children Open after testing positive for COVID-19.
The American's positive test came from pre-tournament screening for the Nevada event.
The 31-year-old last competed in the US Open at Winged Foot Golf Club in Mamaroneck, New York, where he finished tied for eighth.
Finau said on Twitter that he was feeling well and "in good spirits."
"Earlier today, I received a positive result for COVID-19 under PGA Tour on-site testing protocols and have begun a period of self-quarantine to protect others around me."
"I look forward to returning to action as soon as I am able."
Bronson Burgoon will compete in Finau's place, the Tour said.
A handful of competitors have tested positive for the novel coronavirus since the PGA Tour returned in June, including Briton Sam Horsfield and American Scottie Scheffler, who were unable to compete at last month's US Open due to positive COVID-19 tests.
Jason Day leads the Australian charge at TPC Summerlin with Cameron Smith, Greg Chalmers, Cameron Davis, Matt Jones and Craig Hocknull also teeing off on Thursday.
Day, who is aiming for his first victory since the 2018 Wells Fargo Championship, will compete in Las Vegas for the first time since 2012 and is in a group consisting Hideki Matsuyama and Sergio Garcia.
Spaniard Garcia won his first PGA TOUR title since the 2017 Masters at last week's Sanderson Farms Championship and makes his first start in the Shriners Hospitals for Children Open since 2003.
2011 champion Kevin Na, who defeated Patrick Cantlay in a playoff to also win the 2019 event, has been grouped with the 28-year-old and another American in Rickie Fowler.
Bryson DeChambeau, who captured his fifth of seven PGA TOUR titles at the Shriners in 2018, will make his first start since winning the US Open last month.
The world No.4 has two wins in his last eight starts and three consecutive top-10s at TPC Summerlin.