City, who begin their Premier League title defence against Southampton on Sunday, were without the controversial forward for six months of last season following a bust-up between the player and manager.
The pair managed to put their differences to one side towards the end of the last campaign, however, and, with the 28-year-old handed a place in City's line-up on Saturday, it now appears that Mancini is ready to trust Tevez again.
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"Also this year he wants to play football. For a player, it is difficult when he does not play. Last season he did not play for six months and this is difficult.
"I expect him to be a very important player. He is a top player if he wants to play.
"Last year we had Carlos for the last 10 games and it was important because he scored five or six goals.
"But he was not 100 per cent. This year is the first time in four or five years he has done a pre-season and, for every player, this is important."
Whilst the City manager admitted to being happy with his team's performance on Sunday, the 47-year-old did concede that the task was made easier following the first-half dismissal of Branislav Ivanovic for a rash challenge on Aleksandar Kolarov.
Mancini added: "It was a good performance. When Chelsea were leading 1-0, we played better.
"With the sending-off, it was difficult to see from the bench but it is an advantage to play with an extra player.
"It had an impact on the game. It is impossible to say no because 11 versus 11 is different. But we played better than Chelsea, played better football."