Gordon Taylor fears the size and quality of modern squads means Roberto Mancini will not be the last manager forced to deal with an unhappy player.
The Manchester City boss reportedly saw one of his players refuse to step off the substitutes' bench on Tuesday night, as Carlos Tevez's act of defiance overshadowed a UEFA Champions League clash with Bayern Munich.
Tevez has since denied the claims, but Mancini has stated that he considers the Argentine's career with the Blues to be 'finished'.
City's Italian coach also saw another of his forwards, Edin Dzeko, react angrily to being hauled off during a 2-0 defeat at the Allianz Arena.
It is understandable for players to want to start games, and then complete them, but they have to appreciate that football is a team game.
PFA chief Taylor admits too many appear to have lost sight of what constitutes being part of a squad, with it likely that many more coaches will find themselves in Mancini's shoes as a result.
He said: "I think a lot more players are going to get upset.
"There will be top players not happy at being substituted, others who are not too pleased at being asked to retrieve a situation. But it is part and parcel of the game now.
"Players have to be professional, although sometimes managers have to be aware of the sensitivities involved too.
"A statement has been made by Roberto Mancini that the player will not play for the club again. Now it is for the owners to deal with."