The England international was dropped from the Manchester City starting line-up in favour of Costel Pantilimon for the 7-0 demolition of Norwich City on Saturday following a series of errors for both club and country.
But Pellegrini feels Hart needed some time away from the starting XI, having been almost ever-present for the Etihad Stadium club in recent seasons, making 123 consecutive top-flight appearances.
"My duty is to see every week who is the best player to play," Pellegrini said.
"Joe needed a rest, it will be useful for him – he's played every match for two years. Every player can have a bad moment.
"I only know that Joe must work very hard and he will have all of the support of me and the goalkeeper coach and the team. He is England’s goalkeeper and I think he will be back.
"I am sure he will return to his normal performance."
City next face CSKA Moscow in the UEFA Champions League on Tuesday.
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