But they are yet to charge anyone for the coin-throwing incident which saw Manchester United defender Rio Ferdinand hit by an object at the end of the match.
Matthew Stott, 21, had to be restrained by City keeper Joe Hart and was arrested following Robin van Persie’s late winner at the Etihad Stadium.
He was subsequently charged with pitch encroachment.
Speaking through his solicitors Stott confessed his guilt – and said sorry to the Manchester United defender.
“I would like to apologise to all those affected by my actions, particularly Mr Ferdinand and the other players,” he said. “I am extremely ashamed of my actions. I have let myself down, my family down, my fellow fans down and Manchester City Football Club.
“I intend to write personally to Mr Ferdinand to express my extreme regret and apologies and also apologise to Manchester United and their fans. I would like to thank Joe Hart for his actions when I came on the pitch.”
Stott’s lawyers claimed their client’s actions were: “a momentary mistake by Mr Stott which has led to him being charged, brought shame on his family, and will bring sanctions on the club that Mr Stott has supported all his life.
“Mr Stott will accept the consequences of his actions. He would like to make clear that he is not the stereotypical drunken football fan but a fan that attends games with his father. He is embarrassed and ashamed of his temporary moment of madness that has brought wider consequences on the club he supports and his fellow fans.”
Meanwhile, the head of English football expressed concern on Monday about the recurrence of racism and crowd trouble.
“It is deplorable to see those incidents and to see Rio Ferdinand with blood on his face is absolutely terrible,” English Football Association chairman David Bernstein told Sky Sports television. “I think it’s disturbing that we’re seeing a recurrence of these types of incidents.
“We’ve had racial abuse issues, the odd pitch incursion, things being thrown at players – it’s very unacceptable and has to be dealt with severely.”
In the past year, there have been several instances of racism by fans at Premier League matches, while Liverpool striker Luis Suarez and Chelsea captain John Terry have served bans for racial abuse.
“It’s very disappointing – so much of football is so good, great things are happening in football as a whole, but these odd incidents get the headlines – and understandably because they are serious matters, they are unforgivable things,” Bernstein said.
“When you think of the millions watching football every week, or involved in football, to see it hijacked by these incidents is awful so we have to deal with it in the strongest way we can. It’s a difficult social problem. I think there’s a copycat thing: something happens and other people copy it and this sort of thing can spiral.”
As the FA investigates Sunday’s incidents, Bernstein is encouraging clubs to impose life bans one anyone found guilty of misconduct at matches.
“It’s important that matters are brought to a head and people understand that there is no room for this in football at all, and we’ll do everything we can within the FA,” he said. “I know the rest of football feels the same, it’s a blot on the game.”