Graeme McDowell has pulled out of this week's Travelers Championship in the USA because his caddie Ken Comboy tested positive for coronavirus.
Northern Irishman McDowell, 40, said he was withdrawing for the protection of others players and his own physical and mental wellbeing.
It was later revealed that Brooks Koepka's Northern Ireland-born caddie Ricky Elliott had also tested positive.
Koepka has also pulled out as has his brother Chase and Webb Simpson.
PGA Tour commissioner Jay Monahan said that four-time major winner Koepka and former US Open champion Simpson had opted out of the Connecticut event because of an "abundance of caution after having tested positive for Covid-19".
The PGA Tour event starts on Thursday in Cromwell, Connecticut.
McDowell had tested negative earlier this week, but his long-time bagman returned a positive test on Tuesday.
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"I'm going to take a test on Wednesday morning and then jump on a private plane," the former US Open winner told Golfweek.
"I'm going to get myself out of here, home to Florida and decide whether I need to quarantine myself from my family."
American Cameron Champ has already tested positive for Covid-19 during pre-tournament screening at the event.
Nick Watney of the United States also tested positive immediately before his second round at last week's RBC Heritage tournament, which marked the sport's return following the coronavirus shutdown.
The PGA Tour is expected to announce results from its full pre-tournament screening programme on Wednesday.
McDowell himself has shown no symptoms. He felt slightly fatigued last week but attributed that to resuming golf and the aftermath of a friend's funeral.
"I'd been through a huge amount emotionally and mentally, and a couple of weeks back into it after a few months off you're going to be a little tired getting your golf legs back," he said. "But the alarm bells have started to ring now that Kenny has failed this test.
"We're a close-knit team. We roomed together last week, we spent six hours in a car. He's carrying the virus so in some way I have to be carrying it too."