The Italian striker spat his dummy out by throwing down his snood and storming off down the tunnel.
But boss Mancini said: "We decided before the game to replace him after an hour. It's his first start after injury and he had a clash of heads.
"He was unhappy but I will explain to him in a couple of days.
"It's not a problem. We want him fit for the next two months as we have a lot of games.
"He played well and didn't have any problems with his knee."