Former champion Padraig Harrington has withdrawn from next week's US PGA Championship in San Francisco.
The Irishman, who won in 2008, said he was "taking the prudent approach" to Covid-19 by staying at home.
Italy's former Open champion Francesco Molinari has also withdrawn from the year's first major at TPC Harding Park, while England's Paul Waring is injured.
Harrington, 48, and Molinari, 37, have been replaced in the field by Americans Talor Gooch and Troy Merritt.
World number 86 Waring is still troubled by a back problem and will be replaced in the field by another home player, Russell Henley.
Englishmen Lee Westwood and Eddie Pepperell have also not travelled to San Francisco for the tournament - which starts on 3 August - despite the late easing of quarantine restrictions for players and essential personnel.
Golf on the PGA Tour returned in June but no spectators are allowed.
The rescheduled US Open at Winged Foot's West course in September will be played without fans.
No decision over crowds has yet been made for the final major of the restructured season, the Masters at Augusta, which is now scheduled for 12-15 November.
Harrington, who has not played competitively since golf was suspended in March amid the pandemic, said: "As Covid-19 currently looks to be under control in Ireland, I am taking the prudent approach by following the guidelines and reducing the risk as much as possible by staying at home.
"Hopefully I'll have many more years to play in the PGA Championship."
According to the latest statistics, the US has had close to four million Covid-19 cases and there have been over 145,000 coronavirus-related deaths.
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