Manchester United face the possibility of disciplinary action from the Football Association after Manchester City striker Craig Bellamy was struck by a coin during Wednesday night's Carling Cup semi-final second leg.
Bellamy fell to the floor in the second half at Old Trafford after a missile thrown from the home supporters hit him on the back of the head. Beer bottles were also thrown at Bellamy but missed the City striker.
Greater Manchester Police had appealed for calm in the build-up to the game after a fractious first leg at Eastlands that saw Carlos Tevez and Gary Neville engage in an exchange of gestures at the touchline.
But the FA could launch an inquiry into the Bellamy incident that soured a game that United won 3-1 to seal their place in the Carling Cup final, where they will play Aston Villa. A spokesperson for United told the Guardian: "Our security thinks they [the perpetrators] were identified and arrested."
United will ban indefinitely any supporters found guilty of throwing missiles and the FA will now study the report of referee Howard Webb and United's own security report. "Once we have the referee's report and asked for a report from the club itself we can establish what, if any, action is merited," said an FA spokesman.
Police also confirmed that 11 fans had been arrested in the build-up to Wednesday's game at Old Trafford. An increased police presence was on display following trouble in the first leg at Eastlands.
Three men, aged 34, 17 and 34, were arrested for section five public order, a 35-year-old man was arrested for criminal damage, a 44-year-old man was arrested for public order and possession of class A drugs, a 35-year-old man was arrested for attempting to enter the ground while drunk and an 18-year-old man was arrested for theft.
Two other men were arrested inside the stadium during the match, one of whom was detained after a plastic bottle was thrown onto the football pitch. The other in connection with offences at a previous match. Two other men were arrested in the city centre.
Assistant chief constable Ian Hopkins said: "The arrests we made prior to (last night's) game and the work we carried out with the clubs has paid dividends. The vast majority of fans have taken on board our messages ahead of the game, making sure it has been a safe evening and one that can be remembered for the football.
"The low number of arrests on the night is testament to the excellent work of all those involved. The vast majority of fans behaved very well and I would like to thank them for listening to the messages we have been giving, to help make the evening pass off peacefully.''