The Metropolitan Police have condemned the violent clashes between Millwall and Everton fans ahead of their FA Cup clash on Saturday as "some of the most shocking football violence we have seen for some time".
An Everton supporter suffered a "life-changing injury" after an attack from a Millwall fan amid ugly scenes in south London before the tea-time kick-off.
The injured man named himself on social media as Jay Burns, posting an image showing a long scar down the right side of his face, while a police officer was also injured.
The Met are also investigating allegations of racist chanting during the match, some of which was captured on video and posted on social media.
Deputy assistant commissioner Matt Twist said: "The disorder which occurred before, during and after the Millwall v Everton Cup match on Saturday, 26 January was some of the most shocking football violence we have seen for some time.
"The abhorrent behaviour lasted a number of hours, involved dozens of people, and resulted in at least one serious injury.
"One man was taken to hospital with a horrific, life-changing injury to his face. One of our officers was also injured, and has now been discharged from hospital.
"We have a highly-skilled team closely reviewing evidence as we speak, and I am confident we will soon know the identities of those involved.
"We will use this evidence and all tools within our power to locate the individuals involved in this ridiculous behaviour, whether they come from London, Liverpool or elsewhere. We will bring them to justice."
Millwall's 3-2 win over the Premier League side was then marred by a video which appears to show home fans engaging in racist taunts of the visitors.
The Football Association has said it is investigating while Millwall have pledged to hand out life bans to any one found guilty.
Lions chief executive Steve Kavanagh said the incidents have ruined the win, but insists the club should not be subjected to an "attack" or the "same old response", claiming the response has been blown out of proportion.
"I have to remember the core support of the club, the vast majority, are outraged by what has gone on here and that is what makes me sad in the attack that is going on," Kavanagh told BBC Radio Five Live.
"Is (is) that these people aren't educated and they just don't understand?
"Millwall Football Club cannot be responsible for educating the whole of south east London and this group of people.
"We need the authorities, the Football Association, Kick It Out, ourselves and other clubs, rather than threatening everyone with ground closures and sensationalising, 'Chuck them out of the cup', and ridiculous notions that are going on....
"We need to all come together and find a way of trying to get this education. Football is fantastic, let's use its place in society to educate people and find a way of doing that and really coming together.
"Don't say, 'Oh let's get Millwall out of the FA Cup', use it as a position to say, 'Let's get with Millwall, they have been doing this for years, they have got organisations set up in place to educate people, let's go and work with them and see how we can help them'.
"It's an area I would like to explore with the FA and Kick It Out, rather than the same old response which is, 'Right, let's have a go at Millwall, let's fine them or do whatever'.
"That's not getting us anywhere.
"This isn't just a Millwall thing, this happens across society, if you try and tell me there hasn't been a this sort of chant in another club this season in this country I won't believe you.
"It's an issue in society, we will take responsibility for our guys.
"We are an easy peg to hang this on, there is a history there and everything something like this comes up it gets blown into huge proportions as is happening now."