The Football Association today confirmed it had written to Roberto Mancini over his criticism of the referee following Manchester City's Boxing Day defeat.
The FA sent a letter to Mancini requesting his observations on his post-match comments in the wake of City's match against Sunderland.
Mancini could find himself charged by the FA if his words are found to have amounted to improper conduct.
Mancini hit out at referee Kevin Friend following City's 1-0 defeat at the Stadium of Light, saying: "Maybe the referee ate too much for Christmas."
The Italian was particularly angry with what he felt was a foul on Pablo Zabaleta in the build-up to Adam Johnson's winner, saying it was "impossible two men couldn't see it" in reference to Friend and his assistant.