After the problems of last season, the Argentinian has been restored to prominence at the forefront of City's attack this term.
He began the campaign with four goals in as many games but then hit a barren spell and has scored just three since.
Two of them came against Aston Villa a fortnight ago but Tevez has had to settle for a place among the substitutes for the past three games.
Mancini said: "No, I'm not disappointed about this form recently.
"About Carlos I can say nothing (critical) because when he plays, even if he is not 100 per cent, he's a fighter, he puts everything he can on the pitch, so I can't say anything against him.
"But it is clear that we want our strikers to be scoring goals and at this moment Carlos is not strong and for this reason he was on the bench in the last three games.
"But on Saturday that could change, or in the derby. He's not 100 per cent because he has played many games and that is why at the moment he is not so good."
City take on Everton at the Etihad Stadium this weekend before travelling to Germany for their final Champions League group game against Borussia Dortmund.
They then face rivals Manchester United in an eagerly-anticipated derby the following Sunday.
One player Mancini is hoping for more from is playmaker Samir Nasri.
The Frenchman has not made a consistent impact since joining City in a £24million move from Arsenal last year.
The 25-year-old was also left out of the squad for the midweek trip to Wigan as a precaution against a calf problem.
Mancini said: "In my opinion we are talking about a top, top player here.
"If he wants he can change every game, but I think he can do better.
"He has played some good games for us but he can do better because he has everything.
"I don't think he has struggled.
"We are talking about a player like Nasri or (Yaya) Toure or (David) Silva - we always think they can change every game they play because they are capable of doing that.
"But sometimes in spells when we are playing a lot of games in a short space of time, like at the moment, a player can be tired.
"Samir also had a problem with his calf in the last two games but I wait for him to play always a fantastic game because he can do this."
The Manchester clubs have opened up a gap at the top of the Premier League with Chelsea now six points behind second-placed City.
That has led to some seeing the title race as a fight between City and United but Mancini is not writing off the prospects of the Londoners.
When asked if Chelsea can still compete, Mancini said: "Yes they can. Why not?
"They had done a good job until recently. They have a strong team and strong mentality.
"The season is long and in February, when the Champions League starts, everything can change."