Manchester United striker Romelu Lukaku was reportedly at the heart of the post-match fracas that marred his side's 2-1 defeat to Manchester City at the weekend.
The Belgium international, who inadvertently set up both opposition goals during the lively game, is said to have rushed to the defence of manager Jose Mourinho when matters spilled over in the tunnel area.
Both clubs and the Football Association are investigating the incident, which is said to centre around Mourinho entering the away dressing room to tell City's players to mute their celebrations.
According to The Telegraph, Lukaku acted "like a second-row rugby player" as he attempted to get to the Citizens' players during the unsavoury bust-up that could land the rival clubs in trouble.
United's first home loss in 41 games leaves them 11 points adrift of City at the top of the Premier League table.