Vasek Pospisil has resigned from the ATP Player Council amid reports a breakaway body is set to be formed.
The New York Times reported on Friday that world number one Novak Djokovic and the top men's players are creating a players' association.
Amid reports president Djokovic had resigned, Pospisil confirmed on Twitter he had stepped down.
"After two years on the ATP Player Council, I am resigning from my position as the player representative for the 51-100 ranking positions," the Canadian wrote.
"It has become clear that, as a player council member within the current structure of the ATP, it is very difficult, if not impossible, to have any significant impact on any major decisions made by our tour.
"I am proud to say I have always fought for what I believed to be right and, in doing so, never compromised my integrity.
"My sole mission on the council was to represent my peers well, and I'm extremely proud to have done that to the best of my abilities. I leave holding my head high."
Djokovic and Pospisil will serve as initial co-presidents of the new body, according to The New York Times.