The Football Association has written to Manchester United boss Sir Alex Ferguson to ask him to explain comments he made about referee Alan Wiley.
The Scot lambasted Wiley's fitness levels after watching his side snatch a dramatic 2-2 draw against Sunderland.
"The pace of the game demanded a referee who was fit. He was not fit. It was ridiculous," said Ferguson.
However, Blackburn boss Sam Allardyce faces no further action after his criticism of referee Peter Walton.
Allardyce was unhappy with Walton's decision not to give Rovers a penalty in Sunday's 6-2 defeat at Arsenal.
While managers are allowed to make comments on an official's performance, the FA insists they must not imply bias, question their integrity or engage in what could be construed as a personal attack.
I see that once again comments made by SAF are being reviewed by the FA. I don't know why they bother
spursboomer
Ferguson's comments suggested that Wiley was not fit enough to keep up with the pace of the action at Old Trafford.
"You see referees abroad who are as fit as a butcher's dog. He was taking 30 seconds to book a player," added Ferguson, who was also critical of Wiley's decision-making.
Ferguson twice headed towards the touchline during the second half to make his feelings known about decisions made by the officials.
At one point, after he felt midfielder Anderson had been denied a penalty, he jabbed his finger at fourth official Mike Dean and then pointed angrily to the pitch.
As for Allardyce, he was angry with Walton for ignoring Thomas Vermaelen's apparent trip on David Dunn when the score was 3-2 to Arsenal.
"It was a blatant penalty," fumed the Rovers manager.
'Blatant pen' was turning point - Allardyce
"In the pressure pot of this league, you have to get major decisions right. If they (the officials) are not good enough, we should find someone who is."
Allardyce said he had no choice but to speak out about Walton's performance.
"I try not to say too much publicly and say it through the system but unfortunately the system is not working so I have to be heard," he said.
"People may say it is bitter or twisted, but I know I am 100% right because I am very professional in what I do. I research everything and [referees' chief] Keith Hackett knows I am right."