Tevez's future has been in doubt ever since he handed in a transfer request last December, a request which he later withdrew.
And although Mancini admits the Argentinian is an important player, he feels it is important players are happy at Eastlands as City look to next season's Champions League.
"He's got a five-year contract but I always say that a player should stay here because he believes in the project and he's happy to stay at the club," Mancini told reporters.
"But if I'm not happy to stay at City I will leave. It's the same for the players.
"If they aren't happy to stay at the club it's better they leave. But this is not just for Carlos, it's for the players in general.
"When you start your job you should be happy because the season is long and there could be a thousand problems.
"I never said that Carlos wants to leave. I said it would be his decision. He has scored 22 goals and that's very important.
"We always say he's an important player for us. But we've got this far because all the players have contributed."
