Manchester United defender Rio Ferdinand was left with blood pouring from his face after being struck by a coin thrown from the crowd in the dying stages of the Manchester derby on Sunday.
As United celebrated Robin van Persie's late winner, Ferdinand was hit by a coin thrown from a section of the home fans at Etihad Stadium. A City fan was also restrained by police after running onto the field to confront Ferdinand, with City keeper Joe Hart forced to intervene.
Ferdinand laughed off the incident offering a humourous tweet on the subject shortly after the game.
"Whoever threw that coin,what a shot! Can't believe it was a copper 2p....could have at least been a £1 coin!" was the reaction offered up by the experienced centre-back, who left the field with an injury that would have been more fitting if it had been inflicted in a boxing ring.
"What a result, 3 points, sweet!" he went on to add on his Twitter page.
City issued an apology for the incident and said they would assist the police with their inquiries.
"We apologise to Rio," said a club spokesperson. "We condemn the actions of the individual concerned. We are reviewing the CCTV with the police and our normal security.
"We will support the police with any investigation and hopefully identify the person as soon as possible."
However, the Football Association has confirmed it has opened an investigation into the incident.
An FA statement read: "The FA is investigating the incident in which an object was thrown from the crowd and hit Rio Ferdinand following Manchester United's third goal against Manchester City on Sunday.
"The FA will liaise with Greater Manchester Police and await the reports of both our crowd control advisor who was present at the game and the match referee."
An FA spokesperson added: "It is disappointing that after a great game and advert for the Premier League that we are discussing this issue. We will work with the clubs and authorities to identify those responsible and support the strongest sanctions available, including life bans.
"We condemn any such acts and it is simply unacceptable that any player is exposed to injury in this way. To witness Rio Ferdinand leaving the field with a cut above his eye to receive treatment is appalling.
"Football in this country has made great progress over recent decades. However, we must maintain the safety and security inside of our stadia and to do this we need to isolate and identify any individuals guilty of offences with strong penalties to act as a deterrent to others."
Earlier in the game, Wayne Rooney had complained about objects being thrown from the stands as he went to take a corner, while late on City striker Carlos Tevez was perhaps lucky not to be shown a red card after lashing out at United's Phil Jones.
Greater Mancheste Police confirmed via their Twitter account after the match that that a fan was arrested at the Etihad Stadium after racist chanting was heard.
As tempers ran high at the final whistle, stewards tried to prevent United's players celebrating in front of their supporters to avoid further issues.
Speaking after the contest, matchwinner Van Persie professed not to have seen the incident with Ferdinand - although United manager Sir Alex Ferguson described the altercation as 'unfortunate'.
"It's unfortunate toward the end that the City fan runs on and throws coins at our players," Ferguson said. "I don't think you need that.
"The same thing happened at Chelsea which was masked really by all the other things that happened. Two fantastic teams today I think and a fantastic game of football and it could do without that."