Players react after Manchester United's Ander Herrera is shown the yellow card during Sunday's derby. Photo: Martin Rickett / PA

MANCHESTER - The dramatic scenes as a furious dressing-room bust-up erupted at Old Trafford after the Manchester derby can be revealed.

Players traded insults and punches as City celebrated a 2-1 win over United to go 11 points clear at the top of the Premier League on Sunday.

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 brawl between 20 or 30 players and staff from both teams.

"Jose went absolutely ballistic when the bottle hit him," a source said on Monday. "There was steam coming out of his ears, and then everyone waded in."

Michael Carrick tried to act as a peacemaker as the trouble flared and could be heard screaming "Show some f***ing respect" at the City players.

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 fall-out from the extraordinary altercation continued on Monday with the FA formally asking both clubs to give their observations. They have until 6pm on Wednesday to respond. Greater Manchester Police are unlikely to take the matter further after officers who witnessed the incident said they were satisfied no further action was needed.

Privately, United players were accusing City of "lacking class" when they returned to training yesterday. "City were celebrating like they’d won the league," said the source. "They were the better team and deserved to win but you can’t start behaving like that.

Like a rugby 'scrum'

The trouble started when United became irked by City’s exuberant celebrations, and the two sets of players began exchanging insults in Portuguese and Spanish along the corridor that separates the two dressing rooms. Mourinho stormed towards City’s changing area to remonstrate with their opponents and quickly became involved in a heated altercation with Ederson at the entrance.

Mourinho told the Brazilian goalkeeper to show more respect and United also accused him of feigning injury to waste time after Lukaku’s late effort hit him in the face and he recovered to make a stunning follow-up save from Juan Mata. The United manager was then hit on the head by an empty bottle and squirted with water. His players initially thought Ederson was the culprit, but it was actually thrown from the dressing room behind him.

Rojo, who had to come off at half-time after cutting his head in a collision with David Silva, was first down the corridor to support his manager, closely followed by Antonio Valencia, Marcus Rashford, Axel Tuanzebe, Ander Herrera and Luke Shaw.

The City players rushed out of their dressing room and what was described as a "rugby scrum" formed in the corridor.

"The players were pushing each other up and down, with everyone trying to find the room to punch one another," said the source.

One is believed to have landed on Fernandinho, while City captain Vincent Kompany and match-winner Nicolas Otamendi were heavily involved. Others, like Sergio Aguero and Bernardo Silva, kept a safe distance.

City defender Fabian Delph could be seen glancing over his shoulder as the trouble erupted while he and Kevin De Bruyne — who was also delayed by a dope test — gave a live TV interview to Sky Sports after the game.

Coaching staff from both clubs became involved and members of Mourinho’s backroom team were showered with milk when a one-pint carton used to make tea and coffee was thrown in the manager’s direction.

The altercation lasted for no more than two minutes before security staff intervened and order was restored.

As the situation was defused, Mourinho was seen heading towards the referee’s room just yards away to discuss some of Michael Oliver’s decisions.

The United boss, who accused City players of diving in the build-up to the game and branded them "lucky" afterwards, was unhappy that his team were not awarded a penalty for Otamendi’s late challenge on Herrera.

The door to the referee’s room remained closed throughout the trouble, with a policeman standing guard outside. Oliver and his team of assistants did not witness the incident and it was not included in his match report to the FA.

There are no CCTV cameras in the tunnel at Old Trafford, as was the case when United and Arsenal players clashed in the infamous Battle of the Buffet in October 2004 when Sir Alex Ferguson was hit by pizza now admitted to have been thrown by Cesc Fabregas.

But based on widespread reporting, the FA decided to ask for both clubs’ version of events. They have also asked United for their observations after a red flare landed near City substitute Bernardo Silva as he was preparing to take a corner in injury time.

Arteta covered his wound with a hand to prevent photographers taking a picture when he arrived at City’s football academy for training.

Meanwhile, senior United players expressed regret that their team-mates had become embroiled in such an unseemly situation.

They believe it would have been better not to get involved and instead to have stored up the pain and frustration of seeing City celebrate such an important win as a motivational tool when the teams meet again at the Etihad in April.

Some even wondered if Mourinho had instigated the row as a way of galvanising his squad.

The United manager and City boss Pep Guardiola will speak publicly on Tuesday for the first time since the incident came to light when they give press conferences for Wednesday night’s matches. United host Bournemouth while City travel to Swansea.

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