The FA has written to Jose Mourinho asking him to explain comments he made about referee Anthony Taylor in the build-up to Manchester United's 0-0 draw with Liverpool on Monday, reports Sky Sports.
The appointment of Taylor, who is from Wythenshawe in Greater Manchester and supports non-league club Altrincham, was questioned by some Liverpool fans after it was announced.
Managers and players are not allowed to make any comments which could be viewed as intimidatory or influential about the appointed match officials before a game.
The FA has asked Mourinho for his observations on his comments and he has until Friday to respond.