Tiger Woods expressed his gratitude after seeing several male and female golfers show their support on Sunday.
The 15-time major winner, 45, is recovering from leg injuries sustained in a car accident last Tuesday.
“It is hard to explain how touching today was when I turned on the TV and saw all the red shirts,” Woods tweeted.
“To every golfer and every fan, you are truly helping me get through this tough time.”
McIlroy, Tommy Fleetwood, Patrick Reed and Tony Finau wore red and black while competing at the WGC-Workday Championship in Florida, which was won by USA’s Collin Morikawa.
Phil Mickelson did the same at a PGA Tour Champions event in Arizona, as did Annika Sorenstam at the LPGA’s Gainbridge Championship.
“I guess for us it’s just a gesture to let him know that we’re thinking about him and we’re rooting for him,” said McIlroy, 31.
“Things are looking a little better today than they were on Tuesday, but he’s still got a ways to go.
“If there was no Tiger Woods, I just think the tour and the game of golf in general would be in a worse place. He’s meant a lot to us; he still does mean a lot to us.”
Morikawa’s victory at The Concession in Bradenton saw him join Woods as the only players to win both a major and the WGC title before turning 25.
“Tiger means everything to me,” said Morikawa, 24. “I don’t think we say thank you enough, so I want to say thank you to Tiger.”
Woods faces a long period of recovery but was reported to be “in good spirits” after being moved to a new Los Angeles hospital for treatment on Friday.
He was already recovering from his fifth back surgery and hoped to be able to compete at the Masters in April.