By ADAM SHERGOLD and SAM WEBB
Manchester United defender Rio Ferdinand was hit in the head by a coin thrown from the crowd as his team's derby clash with Manchester City ended in an ugly clash.
Ferdinand was left bleeding from his left eye following the incident which took place in the aftermath of United's injury-time winning goal in their 3-2 victory at the Etihad Stadium.
In extraordinary scenes, a City fan then ran on to the pitch to confront Ferdinand but was restrained by Manchester City's goalkeeper Joe Hart. A smoke flare was also thrown onto the pitch.
However, the Premier League star joked about it afterwards, tweeting: 'Whoever threw that coin,what a shot! Can't believe it was a copper 2p....could have at least been a £1 coin!'
He later added on Twitter: 'Respect to Joe Hart for protecting that idiot who ran on!! Love the banter between fans but there is a point when it goes too far...calm it!'
Manchester City has apologised to the player and the Football Association has launched an investigation.
Ferdinand's team-mate Ashley Young told MUTV: 'It could have taken Rio's eye out and you've seen the cut on his head.
'When 'Wazza' (Rooney) was taking a corner there were so many objects being thrown on to the pitch as well and, on another day, if the pitch had not been so wet, the fan who came on to the pitch wouldn't have slipped over and could have attacked Rio.'
In a statement, the club said any fans found responsible would be disciplined, adding: 'Manchester City FC security officials are co-operating fully with Greater Manchester Police in relation to events leading up to the throwing of missiles onto the field of play, and between the two sets of supporters, during today's game against Manchester United.
'Manchester City wishes to offer its sincere apologies to Rio Ferdinand. The club unreservedly condemns the actions which led to his being injured.'
United manager Sir Alex Ferguson said: 'It's just unfortunate... [that] a City fan runs on and then they throw coins at our players.'
City trailed 2-0 but fought back to equalise before Robin van Persie's late free-kick secured three points for their arch-rivals.
But the match was marred by the serious security lapse - and the arrest of a man over alleged racist chanting.
Greater Manchester Police confirmed after the match that a man was arrested inside the Etihad Stadium following allegations of racist chanting.
Stars Tom Cruise and Robert Duvall were at the game. They are in the country to attend the premiere of Tom Cruise's latest film Jack Reacher.