"My duty is to see every week who is the best player to play," Pellegrini told the club's official website.
"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."
The win has lifted Manchester City up to fourth place in the Premier League table.