Manchester City has apologised to Rio Ferdinand after he was hit above the left eye by a two-pence coin thrown from the crowd near the end of a heated derby clash with Manchester United.
The club said it "unreservedly condemns" the incident which took place as the defender celebrated his team's last-gasp winner in their 3-2 Premier League away victory.
With blood pouring down his face there was more controversy when a City supporter ran on to the pitch to confront Ferdinand.
The fan slipped and fell as he approached the player and then England and City keeper Joe Hart stepped in to separate the pair as he restrained the pitch invader who was eventually arrested.
Police are scouring CCTV footage at the Etihad Stadium in a bid to trace the coin-throwing culprit as the Football Association (FA) said it had launched its own inquiry.
Ferdinand, 34, later posted on his twitter account: "what a result, 3points! Sweet! Whoever threw that coin, what a shot! Can't believe it was a copper 2p....could have at least been a £1 coin!"
He then wrote: "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 said its security officials would co-operate fully with Greater Manchester Police over incidents of missiles being thrown on to the field of play and, it said, between the rival sets of supporters.
In a statement, the club said: "GMP's review of all fan behaviour at today's match will be fully supported by the club, through the provision of CCTV footage and eyewitness accounts. Following this review, and any associated police action, the club will also apply its own disciplinary policies for any fans found guilty of offences."
Viewers on Sky Sports, which showed the match live, also saw Manchester United striker Wayne Rooney being forced to dodge an array of objects thrown in his direction as he took a corner. 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."