The Football Association (FA) has asked Jose Mourinho to explain comments he made about referee Anthony Taylor ahead of Monday's 0-0 draw between Liverpool and Manchester United at Anfield.
Omnisport understands United boss Mourinho has until 6pm on Friday to respond to the governing body, at which point the FA will decide whether to charge him in relation to rules prohibiting managers from speaking about referees in the build-up to matches.
In his pre-match news conference, Mourinho said Altrincham-based Taylor would struggle to have "a very good performance" at the centre of United and Liverpool's fierce rivalry due to him hailing from the north west of England
"I think Mr Taylor is a very good referee but I think somebody with intention is putting such a pressure on him that I feel that it will be difficult for him to have a very good performance,'' he said.
After the stalemate on Merseyside, Mourinho asked United's press officer if he was allowed to pass comment on Taylor before praising his performance.
"He had a good game and I am happy for him because people with responsibilities put a lot of pressure on him and it was very difficult for him to have a good performance, which he had," he said.
In May 2011, former United boss Sir Alex Ferguson was the first manager to be punished under the rules introduced in 2009, when he said Howard Webb was "definitely the best referee in the country" ahead of a match with Chelsea.
Mourinho is no stranger to run-ins with the FA over refereeing issues.
As his second Chelsea reign unravelled last season, he was handed a suspended one-match stadium ban and a £50,000 fine for suggesting referees were "afraid" to award penalties to his team in the aftermath of a 3-1 loss to Southampton.
The Portuguese's behaviour towards the match officials during a defeat at West Ham last October saw him sent to the stands and banned from attending a subsequent trip to Stoke City.