Players could strike in their bid to cut down on the number of matches they play, England's Professional Footballers' Association warned FIFA.
Football's world governing body is under growing pressure to address the workload of elite players, with threats of legal action.
The PFA wants action to alter the congested football calendar, especially with the expanded 32-team Club World Cup proposed for next summer.
An event Thursday in London by the PFA and FIFPRO, the international players' union, heard that players were at "breaking point".
PFA chief executive Maheta Molango recalled a recent conversation he had with players of an unnamed club.
"How far would you like to go?" Molango recounted asking the players, according to the BBC.
"Some of them said: 'I'm not having it, we may as well strike.'
"Some said: 'What's the point? Yes, I'm a millionaire, but I don't even have time to spend the money.'"
Molango added: "We have reached a point where we cannot discount any action."
Alexander Bielefeld, head of policy for FIFPRO, told the BBC the results of the the annual player workload review are "staggering".
He warned that it is going to only increase next season.
"We are ahead of the worst season in terms of new fixture calendar, with the new Uefa Champions League format kicking in and also the (expanded) Club World Cup entering the calendar," saoid Bielefeld.
"There is the ability to more evenly attribute workload and matches amongst players and also amongst young talent.
"We do not do it because the pressure — I think on everyone — is so high, even if medical staff advise the coach not to play the player or to sit him out. The pressure on the coaches and the player is so high that they will play anyway."
FIFA was already facing the threat of legal action if there is no rescheduling of the 2025 Club World Cup.
A letter recently sent to FIFA president Gianni Infantino by the World Leagues' Association and FIFPRO said football's worldwide schedule was now "beyond saturation".
FIFA in response said it would guarantee player welfare with its "harmonious" scheduling.
The football schedule will expand once more next season, with the Champions League and Europa League having eight first-phase games compared to six this term.
The Champions League, Europa League and UEFA Conference League will all be increased to 36 teams.
"The unions feel more compelled than ever that something has to be done about player workload — it has to be regulated," said Bielefeld.
AFP