The Football Association wrote to Mancini following his claim that "maybe the referee ate too much for Christmas", as Friend missed what Mancini felt was a clear foul on Pablo Zabaleta in the build-up to Adam Johnson's winner.
Due to a busy festive period, the judicial panel granted Mancini's request for an extension and it is thought the City boss is facing either a warning or fine for his reaction.
While City have made their frustration known at the investigation as Sir Alex Ferguson escaped without punishment for his behaviour during Manchester United's win over Newcastle the same day, it has been pointed out by the FA that there are clear differences.
Mancini delivered his assessment after the game and Friend was not present - unlike fellow referee Mike Dean, who described his own clash with Ferguson before the second half of United's 4-3 victory as 'cordial'.
In addition, whilst Mancini's comments could be viewed as an amusing aside, they have called into question Friend's competence which the FA, at the very least, feel demands clarification.