Manchester City boss Pep Guardiola has been asked by the Football Association to explain comments he made about the referee before Sunday's derby with Manchester United.
Premier League bosses are not to speak about match officials before fixtures.
But before his side's 3-1 home win, Spaniard Guardiola responded to a question that suggested Anthony Taylor might be biased in United's favour.
He has until 18:00 GMT on Thursday to respond.
Guardiola had said: "He is going to try to do the best job like we try to as managers and football players.
"Mr Taylor is going to try to have a good game. The important thing is to focus on our game and, of course, knowing which opponent we are going to face and that is all.
"Hopefully he can make good decisions for both sides and it will a good game. All England and all Europe is going to watch us. That is the most important pleasure."