The News of the World says while Mark Hughes was still manager, City put together a compilation of some of the player's worst tantrums.
City's top officials, including Hughes, watched a DVD which showed Balotelli sulking during matches and 'behaving like a spoilt kid', according to one person who saw it.
The source said: "In one game, Balotelli just sat down on the pitch with his hands on his knees, shaking his head, apparently because someone had not passed to him. The game just carried on around him.
"There were lots of examples of him acting as if he was the only person who mattered and wanted everyone in the crowd to look at him. There is no doubt he has talent, but his attitude leaves a lot to be desired."