McDowell won the 2010 US Open at Pebble Beach in California
Graeme McDowell pulled into this week's Travelers Championship in the US because his caddy Ken Comboy tested positive for coronavirus.
Northern Irishman McDowell, 40, said he withdrew for the protection of other players and his own physical and mental well-being.
The PGA Tour event kicks off Thursday in Cromwell, Connecticut.
McDowell had tested negative earlier this week, but his old bagman returned a positive test on Tuesday. told Golf Week
"I'm going to take myself out of here to Florida and decide if I should quarantine myself with my family."
The American Cameron Champ has already tested positive for Covid-19 during the pre-tournament research during the event.
McDowell and Comboy spent six hours together in a car on Friday
Nick Watney from the United States also tested positive just before his second round at last week's RBC Heritage tournament, which marked the sport's return following the closure of the corona virus.
The PGA Tour is expected to release the results of the full pre-tournament screening program on Wednesday.
McDowell himself did not show any symptoms. He felt a little tired last week, but attributed that to the resumption of golf and the aftermath of a friend's funeral.
"I had been through a tremendous amount of emotional and mental health, and a few weeks after a few months off, you will be a little tired to get your golf legs back," he said. "But the alarm bells are ringing now that Kenny has failed this test.
" We are a close-knit team. We were staying together last week, we spent six hours in a car. He's carrying the virus so somehow I have to carry it too. "