The England goalkeeper was dropped for the 7-0 victory over Norwich City after a number of high-profile errors at the start of the 2013-14 campaign, the first time since April 2010 that Hart has missed a Premier League game.
Pantilimon had little to do in the emphatic win at the Etihad Stadium on Saturday although looks set to continue between the sticks for City's Champions League meeting with CSKA Moscow on Tuesday.
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"Joe made a lot of mistakes, he knows. Not just this year, also last year. So I think for Joe it’s a good moment to stop.
"But I have confidence in Costel, that’s why he’s the second goalkeeper. If I don’t have trust in him I will change it. It’s done and I am sure he will do very well.
"It’s not an answer to do in just one minute. He has had several things that normally happen to goalkeepers."
Pellegrini has not shut the door on Hart, however, insisting he is confident the England No.1 will eventually earn his place back in the City starting XI.
He added: "I’m absolutely sure that working hard he will – I don’t know when – return to his normal position.
"We will try to recover him as soon as possible. But he was the first player today [against Norwich] who congratulated Costel and the morale inside the team is very, very well.
"Joe is one of the players with him and my duty is to start with the players I think that will give the best performance."