Mancini told reporters: "I think that Rafa is a good manager. He doesn't deserve all the bad things that he has there. He has worked hard, worked well for Chelsea.
"But football is strange. He is one of the best managers and Chelsea are one of the best teams. They won the Champions League last season.
"I think Rafa knows us well and we know Chelsea well. We know the players but tactics will play a big part."
City and Chelsea face off later today in the last four of the FA Cup at Wembley.