An altercation between Manchester City striker Craig Bellamy and a Manchester United fan during Sunday's dramatic derby is being investigated by Greater Manchester Police and the FA.
Following Michael Owen's winning goal deep into injury time at Old Trafford, a United fan was seen to enter the field of play as City took their kick-off and was involved in an angry exchange with Bellamy.
The striker, who scored twice in the 4-3 defeat for his side, appeared to shove the pitch invader in the face before being confronted by Manchester United defender Rio Ferdinand.
"At the end of the derby between Manchester United and Manchester City at Old Trafford, a member of the public ran on to the pitch, and was detained by police and security staff," said a Greater Manchester Police spokesman. "During this time, there was an altercation between the man and a player from Manchester City FC."
The fan has been charged with unlawfully running onto the pitch and will appear in court later this month.
Manchester City assistant manager Mark Bowen has said the club will not be taking any action against Bellamy but, in the wake of Emmanuel Adebayor's recent three-match suspension, the FA will scrutinise the behaviour of another City striker.
An FA spokesman said: "We are investigating the incident and we will be looking at the referee's match report.''
City boss Mark Hughes laid the blame with the United supporter who made his way onto the pitch and joked about a similar incident involving Nottingham Forest manager Brian Clough in 1989.
"I seem to recall Brian Clough clipping someone around the ear, and he was lauded as a national hero,'' said Hughes. "Maybe it will be the same case with Craig - but I doubt it.
"I'm sure people will make a nuisance about it, but the guy should not have been on the pitch. That is not acceptable.''
Police will also investigate an incident that saw Manchester City defender Javier Garrido struck by a coin at half-time, with the missile apparently intended for Carlos Tevez on his first game at Old Trafford following his summer move to City.
Hughes said: "Something came from the crowd, but he [Garrido] is okay."