Everton boss David Moyes is unimpressed that Mike Riley will referee Sunday's FA Cup semi-final with Manchester United at Wembley. The Yorkshire official is a late replacement for Steve Bennett, who has withdrawn due to illness.
But Moyes has raised the suggestion that Riley is a fan of United.
He said on the club's official website: "A member of the press asked me if Mike Riley is a Manchester United supporter - I think that is something you would need to bring up with the FA.
"It is something that one or two managers would have something to say about. It is the FA's appointment; it was originally supposed to be Steve Bennett.
"If you (the press) are saying that Mike Riley is a Manchester United supporter, you would hope the FA would look at that."
Moyes added that, in general, he believes English referees are doing a good job, but he did question the influence of the so-called 'big four'.
He said: "Referees in this country are very honest. They try to get the decisions right.
"I think they can be influenced, I think that has been seen in a couple of games I have been involved in recently."
A FA spokesman said: "All our referees are fair, unbiased and objective.
"Mike Riley is one of our top officials and we are 100% confident he will do a good job on Sunday."