Four-time major champion Brooks Koepka and past US Open winners Webb Simpson and Graeme McDowell are among six golfers who won't compete the US PGA Travelers Championship after three COVID-19 positive tests at the event.
US PGA commissioner Jay Monahan has tightened restrictions in the tour's health and safety plan in the wake of positive tests by US player Cameron Champ, McDowell caddie Ken Comboy and Koepka caddie Ricky Elliott.
"I haven't tested positive for COVID-19, but as I've said all along, I'm taking this very seriously," Koepka said. "I don't want to do anything that might jeopardize the health of any player in the field or his ability to compete.
Fourth-ranked Koepka is set to seek a third consecutive PGA Championship title in August.
"The right thing to do right now is get home, support Ricky and feel confident that I'm doing what I can do protecting my fellow tour members," Koepka said.
Americans Cameron Champ, Nick Watney and Chase Koepka are the other golfers who will miss the event starting Thursday at TPC River Highlands in Cromwell, Connecticut, in the tour's third event back from a three-month coronavirus shutdown.
"We all need to learn to live with this virus. It's pretty clear this virus isn't going anywhere," Monahan said.
"We're going to have more positives going forward. We're just going to continue to refine (safeguards) and get better and better and find new ways to mitigate the risk."
Watney tested positive last week in South Carolina. Champ was positive on Tuesday. Comboy and Elliott tested positive after Koepka, his younger brother Chase and Northern Ireland's McDowell practiced together Tuesday.
"I have experienced some fatigue and muscle soreness myself," 2010 US Open winner McDowell said. "I didn't think of it as COVID related... but now that Kenny has tested positive... I have to take those symptoms more seriously.
"I'm not keen on risking the possibility that I could pass it onto anyone else this week."
Simpson, the 2012 US Open champion who won last week's Heritage title, tested negative twice for the deadly virus but withdrew after a family member tested positive. He plans to quarantine in North Carolina.
Tighter protocols include additional tests upon arrival in every event city and bringing the tour's fitness trailer on site each week so golfers avoid gym visits.
"We will probably continue to make adjustments. The changes we've made this week are a very good step," said Monahan. "We're going to make sure we take time to reinforce the strong protocols we already have.
"We feel like we're going to be in position to sustain our return."
Monahan promised punishments for anyone not following social distance, masking or other protocols inside the PGA's safety zone.
"For those who do not, there will be serious repercussions," Monahan said. "Consequences will be significant.
"We've gotten a little bit lax or away from protocol. That's the kind of tightening we need to do to make sure we're in a good position moving forward."
- Confident in fan plan -
The PGA plans to welcome back spectators to events in mid-July at the Jack Nicklaus-hosted Memorial in Dublin, Ohio.
"We're confident in that plan," said Monahan, adding, "We're only going to do it if it's a healthy and safe enviroment for our players, caddies and the fans who would be attending."
Monahan says while there are COVID-19 risks in staging events, he doesn't expect so many positives it would force another tour shutdown.
"They are containable and we're going to avoid that scenario," Monahan said. "We're confident in the plan we have and we're hopeful we're not going to be in that position."
Charley Hoffman, a member of the Players Advisory Council, said playing in Texas and South Carolina was "pretty much the wild, wild west" after tight virus safeguards in California.
"We're learning from our mistakes," he said. "We're not perfect. We're working on that daily. We're going to get better and we're going to lead by example.
"If we still want to keep playing golf, we've got to understand this virus."
Four-time major winner Brooks Koepka, left, will not play in this week's Travelers Championship after caddie Ricky Elliott, right, tested positive for COVID-19