The Football Association has written to Sir Alex Ferguson asking him to explain the comments he made about referee Alan Wiley following Saturday's draw with Sunderland.
The Manchester United boss was unhappy with the fitness of Wiley during the 2-2 draw at Old Trafford and accused the referee of 'not being fit enough'.
The FA has since promised to review the comments and the governing body has contacted Ferguson requesting an explanation for his remarks.
Ferguson also claimed Wiley had not played the correct amount of added time because he had failed to add on an additional minute to the four already signalled once United scored.
Wiley was also involved in the controversial Manchester derby last month, in which Michael Owen grabbed a 96th minute winner at Old Trafford to spark debate over how much time should be added for stoppages.
However, no further action will be taken against Blackburn manager Sam Allardyce who criticised Peter Walton for not giving Rovers a penalty in Sunday's 6-2 defeat at Arsenal.