Eventually, he was substituted and headed straight down the tunnel, although not before fixing Mancini with an icy stare.
"The game against United was the final straw," said Marsh to the Daily Star Sunday.
"There is no question that Mario Balotelli is one of the most talented footballers I've seen. If you look at him playing for Italy at Euro 2012 in Poland and Ukraine he was fantastic.
"But in the last three or four months I have seen his attitude, both on and off the pitch, deteriorate. It's not conducive for a good team spirit. He was embarrassing during the first 45 minutes against Manchester United at home.
"He needed to give a big performance to get the result. And he was playing at home in front of his own fans. He started the game instead of Carlos Tevez but City were two-nil down when he came off and they couldn't recover.
"From that point on he's hardly played a game."