The Football Association has asked both Manchester United and Manchester City for their respective observations following the post-match altercation after Sunday's derby at Old Trafford.
Both coaches and players are thought to have clashed in the tunnel following City's 2-1 victory at the Theatre of Dreams, in an incident that is understood to have left City assistant Mikel Arteta with a cut to his head.
Other reports have claimed that United boss Jose Mourinho was left covered in 'milk and water' during the melee, which is reported to have emerged after Mourinho took exception to what he deemed as excessive celebrations from City.
The row was not included as part of referee Michael Oliver's report of the game, although the FA has now asked both clubs to explain the incident.
United and City have until 5pm on Wednesday to respond.
