The Italian made a comment to matchday coach Angelo Alessio after being replaced by Sebastian Giovinco and chief executive Giuseppe Marotta has confirmed the 29-year-old was punished for the reaction.
“Quagliarella was fined but only after a calm discussion with him,” he told Sky TG24.
"He was angry at being substituted in a game where the team were losing - he wanted to help his team-mates to get an equaliser. It was an anger that immediately passed.
"The club have strict rules in terms of behaviour, and cannot allow misconduct."
Marotta went on to play down reports suggesting that Claudio Marchisio and Leonardo Bonucci were involved in a heated exchange after the final whistle.
"Nothing happened between Marchisio and Bonucci."
Robinho's penalty just after the half-hour mark was enough to give the Rossoneri the points at San Siro.