Hart was replaced by Costel Pantilimon after a number of errors this season and Zabaleta understands that it could happen to anyone in the squad.
"Well, you know, that is football. The manager makes decisions," Zabaleta told reporters.
"We know in this team now the performance of everyone should be good week in, week out because we have two players in each position who can play.
"Sometimes mistakes might cost the place but we are a big squad and we need to try to do well to keep the place in the team."
City face CSKA Moscow in the Champions League on Tuesday night.