Manchester United boss Sir Alex Ferguson is facing an FA investigation over his attack on referees' chief Keith Hackett.

Ferguson slammed Hackett after Chelsea skipper John Terry had a red card and three-game ban overturned.

Fergie accused Hackett of bias, claiming he had put pressure on referee Mark Halsey to overturn the sending-off at Manchester City last Saturday.

But yesterday the Professional Game Match Officials Board, which Hackett heads, said he had no bearing on the decision to overturn the sending-off.

A PGMO spokesman said: "All matters of discipline are an issue for the FA - and them alone."