London (AFP) - The Football Association demanded answers from Manchester United and Manchester City on Monday (Dec 11) following reports of ugly scenes that reportedly left City assistant coach Mikel Arteta bloodied after a fracas.

The Guardian newspaper said Arteta was left with blood streaming down his face after a bust-up involving up to 20 players and members of staff from the two clubs after Sunday's (Dec 10) Manchester derby, which City won 2-1.

Referee Michael Oliver did not witness the scenes so the FA has not received a report on the matter from him, but it has given the clubs until Wednesday (Dec 13) to reply to a request for observations following the incident.

United manager Jose Mourinho and City goalkeeper Ederson are reported to have had a confrontation after the game, while it is claimed Mourinho had milk and water thrown at him from the away dressing room.

The home side are understood to have taken exception to City's post-match celebrations.

The Guardian reported that Arteta's eyebrow was split open during the melee in a narrow corridor outside City's dressing room and said there were unconfirmed reports that another member of Guardiola's backroom staff needed medical treatment.

The corridor leading to the dressing rooms apparently became congested as players and staff made their way through it after the game, and tensions spilled over into pushing and shoving, with Arteta understood to have suffered a cut to the head.

Mourinho did not make any reference to what had happened during his post-match media work, according to the report.

Arteta was assessed in the City dressing room after being caught in the crossfire, the report said.