Mancini kicks off his reign at City against Stoke City today.
Mancini once got changed at half-time and refused to play the second half of an Italian League game for Sampdoria after a dressing-room row with the club president.
"Mancho was a god when he was at Sampdoria," said a source close to Mancini to the Daily Express.
"But he could run 30 yards in a game to tell someone off. He turned on a younger player during one match and continued that in the dressing room.
"When he was told he was out of order to turn on a younger player, that was it, Mancho took his shirt off and said he wasn't playing. It took a team-mate to persuade him to go out again.
"So Mancho dried his hair, put on a new shirt and played."
Mancini was also known for being difficult as a player, moaning and grumpy. So he should get on with Craig Bellamy at City.
"But also Mancini won't waste a minute of his time," said the source. "He is a very good coach. He makes a winning mentality in the dressing room. He won't be like the English managers and want to do all the transfer deals.
"Mancho will be on the training pitch all the time. He won't waste a second. He won't have waited until the last minute to bring up Rory Delap's long throw for Stoke.
"That will have been worked on during intense 20 or 30-minute sessions with the players from the moment he got to City.
"Robbie also likes to work with a small group of players. When he went to Inter Milan as manager he found there were 54 players. He chose the ones he wanted to be with him and another trainer was brought in to deal with the rest.
"Mancini will work with 20 to 23 players, that's all he needs."