"After some of the situations I saw in the last three or four weeks, I think it is really difficult for us. The rules are not the same for everyone," said Mancini.
Patrick Vieira, who is currently Football Development Executive at City, previously stated his belief that Manchester United are given preferential treatment by officials, but Mancini refused to state the same opinion so openly.
"I am not saying this, I don't want to say this. I said the rules, maybe sometimes, are different," he added.
"When I was in Italy I always thought here there were the best referees. My idea has changed, probably."
City are currently five points behind their neighbours in the table.