Manchester United boss Mourinho caused controversy during his pre-match press conference on Friday, saying of the City players: "A little bit of wind and they fall."

He then questioned Pep Guardiola’s permission to wear a yellow ribbon - a symbol of protest against the imprisonment of pro-independence politicians in the Spanish region of Catalonia - on the touchline.

And in a conversation with the Sunday newspapers, Mourinho warned match referee Michael Oliver of City’s “tactical fouls”.

United lost Sunday’s game 2-1 in a major blow to their title hopes.

The Football Association have requested observations from Mourinho regarding Friday’s press conference.

He has until 6pm on Monday to respond.

Mourinho was unhappy with the result of the derby and had an altercation with City players and staff after the game, which resulted in milk being thrown on the Portuguese boss.

He laid into referee Oliver after the game, blaming him for booking Ander Herrera for simulation rather than awarding a penalty.

"My first reaction is I feel sorry for referee Michael Oliver because he had a very good match but unfortunately he made an important mistake," he said.

"The result was made with a big penalty not given [on Ander Herrera].

"That would have been 2-2 with 20 minutes to go.

"Michael was unlucky because it was a clear penalty."