The organisation released a report Thursday calling for safeguards to be introduced for players who already face excessive workloads amid a constantly growing calendar.
The report on player workload in men's football underlines concerns over "growing intrusion into their private lives, and a lack of player care by football governing bodies," FIFPro says.
The union suggests bringing in a guaranteed minimum amount of time off, and even the introduction of a maximum number of games for players.
The report is published just before the start of the new, expanded UEFA Champions League which now involves up to four extra games for participating clubs.
The season in Europe is also due to finish with the first edition of FIFA's expanded Club World Cup in the United States, featuring 32 teams.
It is due to take place from mid-June to mid-July, a time when players can usually expect to have some time off in years with no major international tournament.
"The physical and mental well-being of players must be a priority if we want to maintain the integrity of the game," said Stephane Burchkalter, FIFPro's acting General Secretary.
"The cannibalisation of the competition calendar is pushing players beyond their limits and is encroaching on their private lives.
"We need safeguards for players to limit their travel, ensure rest periods, and provide adequate recovery so they can reach peak performance."=
FIFPro's study surveyed 1,500 players and found that 54 percent were already exposed to what it called "excessive or high workload demands".
'Defining season'
It cites the example of Julian Alvarez, who played in 75 games for club and country last season, including appearing at both the Copa America and Olympics for Argentina.
In total he was included in 83 matchday squads, travelling and preparing for these matches even if he did not always appear.
Maheta Molango, CEO of England's Professional Footballers' Association, cited the fine starts to this season of Manchester City's Erling Haaland and Liverpool's Mohamed Salah -- who did not go to Euro 2024 or the Copa America -- as examples of the benefits of having a proper break between seasons.
"It is very nice to go to a dressing room and hear someone say how much they missed training," Molango said.
"It was very telling when you see the feedback from people who have not had that rest.
"They look shattered. That is very worrying and this season will be the defining season.
"The calendar, no matter how you look at it, doesn't make any sense."
FIFPro Europe recently joined together with European Leagues -- a body bringing together more than one thousand clubs from 33 countries, including England, Italy, Germany and France -- to file a complaint to the European Commission accusing FIFA of abusing its position.
FIFA has been accused of a failure to consult over recent changes to the calendar, such as the introduction of the new Club World Cup.
"The projected number of games for these players is only going to increase," said Alexander Bielefeld, FIFPro's director of policy and strategic relations, adding that the number of matches they will likely end up playing was "shocking".
"We simply don't believe that voluntary rest is going to get to the core of this."
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