Manchester City coaches' goading of Manchester United striker Zlatan Ibrahimovic may have caused the explosive Old Trafford tunnel bust-up on Sunday.
Members of Pep Guardiola's backroom staff allegedly picked on the Swedish striker as they made their way back to the changing room.
Spanish newspaper Marca claim they told the 36-year-old: 'Ibra, you talk a lot but you move a little.'
Zlatan Ibrahimovic was allegedly at the centre of the Old Trafford tunnel bust-up on Sunday
Ibrahimovic was a second-half substitute for Jesse Lingard during Manchester City's 2-1 win
United then took that as provocation that sparked the 30-man brawl in the immediate aftermath of City's 2-1 win at the home of their fierce rivals.
Players traded insults and punches as City celebrated a victory that handed them an 11-point lead at the top of the Premier League after only 16 games of the season.
Ibrahimovic has previous with Guardiola and his coaching staff after falling out with them during his one-year spell at Barcelona in 2009-10.
The two failed to see eye-to-eye at the Nou Camp, and Ibrahimovic was moved on at the end of the season.
Pep Guardiola brought Ibrahimovic to Barcelona but the pair fell out at the Nou Camp
The pair failed to see eye-to-eye with the Swede preferring the methods of Jose Mourinho
A few of Guardiola's coaching staff at City worked alongside the Spaniard at Barca, including assistant coaches Dominic Torrent and Rodolfo Borrell, and fitness coach Lorenzo Buenaventura.
Former Arsenal midfielder Mikel Arteta and long-serving Brian Kidd are also involved in the backroom set up.
Sportsmail revealed on Monday that a bare-chested Marcos Rojo led United's players in defence of manager Jose Mourinho after he was hit on the head by a water bottle thrown from the City dressing room, igniting a mass brawl.
Guardiola's assistant, Domenec Torrent (right), worked alongside him at Barcelona
United striker Romelu Lukaku was also accused of throwing a water bottle in retaliation.
City coach Mikel Arteta suffered a cut to his forehead and was spotted with four butterfly stitches in the wound when he dined out with friends in a Manchester restaurant on Sunday evening.
The Football Association have asked both clubs to give their observations by 6pm on Tuesday.