Rory McIlroy described Brooks Koepka as deceitful after the four-times major winner defected to the breakaway LIV Golf Invitational Series on Wednesday.
Koepka, a former world number one, became the latest big name to join the lucrative LIV Series, joining a list that includes six-times major champion Phil Mickelson, former Masters champion Dustin Johnson and former U.S. Open champion Bryson DeChambeau.
Among the PGA Tour's most vocal backers, McIlroy, speaking to the media ahead of this week's Travelers Championship in Cromwell, Connecticut, criticised Koepka and others for turning their backs on the PGA Tour after previously expressing their support.
"Am I surprised? Yes, because of what he (Koepka) said previously," said the Northern Irishman who has moved up to number two in the world rankings following a successful title defence at the Canadian Open and tie for fifth at the U.S. Open.
"That's why I'm surprised at a lot of these guys because they say one thing and then they do another.
"It's pretty duplicitous on their part to say one thing and then do another thing."
The PGA Tour has suspended members who signed up to play with LIV Golf and said others who follow them will face the same punishment.
However, they were able to play at the U.S. Open last week and were given the all-clear by the R&A on Wednesday to tee it up at The British Open at St Andrews from July 14-17.
The LIV Series will play its first American event in Portland, Oregon from June 30-July 2 at the Pumpkin Ridge Golf Club, going head-to-head with the PGA Tour's John Deere Classic.
LIV Golf held its first event in London this month which was won by South Africa's Charl Schwartzel, who pocketed the $4 million prize -- the biggest pay cheque in golf history.
PGA Tour commissioner Jay Monahan accused the LIV Invitational Series of attempting to buy the game of golf then went on the offensive, unveiling larger purses, new events and a different calendar.
Also speaking at the Travelers Championship, Monahan conceded that the PGA Tour cannot compete when it comes to cash but announced it would increase purses at eight events during the 2022-23 season to an average of $20 million.