"If a top player is not happy to stay here then it's better to go to another team," the manager told reporters. "I think this is not just the case for Tevez, but for all players."
Tevez complained about Mancini's double training sessions last week and reports have suggested the Argentine is seeking an improved deal, even though he has four years of his contract to run. Some say he might consider his future if City fail to secure Champions League qualification in the final three games.
"It is important that, when a manager or player works in a team, he must be happy to work in this team," Mancini said.
"It's not good for the club, for the squad or for the player if he is not. I don't know if Carlos Tevez is unhappy but he must be content because we have to play three important games.
"For the players, it is a crucial moment. They must put everything they have on the pitch.
"Tevez has four years left on his contract," he added. "If he's not happy, it's better to change squads, not just for Tevez but for all players as well."
Mancini said he did not understand Tevez's complaints about training. "We trained twice in the same day only four times in five months. Two of those times Carlos was in Argentina, one time he didn't train.
"I don't know why (he's unhappy). When we don't have a midweek game I always train two times on Tuesday because it's the only way I know. By working we can improve, but we won't improve if we work two days and have one day off."
Mancini said he had spoken to the striker. "I don't know if he has a problem but he works very well now. I spoke with him but what we said is private.
"I reminded him that he only had to train twice in a day once.
"I hope Carlos can score three or four goals in the next three games, and afterwards we can decide if he has a problem."
City are sixth in the Premier League, one point behind Tottenham and Aston Villa, and host Villa on Saturday.
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