The FA has launched an investigation into reported racist chanting by a section of Millwall supporters in the club’s 3-2 FA Cup win over Everton.
A video showing a group supporters using racist language in a song directed at Everton fans circulated on social media after the match.
The footage shows dozens of supporters chanting during the game, taunting Everton fans with a song featuring racist language about people of South Asian descent.
An FA statement read: "The FA can confirm that we are aware of video posted on social media after The Emirates FA Cup match between Millwall and Everton. Discriminatory behaviour and chanting has no place in football and we will be investigating the matter."
Millwall said they will issue lifetime bans to any supporter found guilty of racist abuse during their match with Everton.
A club statement read: "Millwall Football Club is aware of, and extremely disappointed by, a video circulating online displaying alleged racist chanting during Saturday's victory over Everton.
"The club will, as is commonplace following such incidents, work with all relevant authorities during investigations into the matter and look to identify individuals involved. Anyone identified and guilty of such abuse will be banned from The Den for life."
Anti-discrimination group Kick It Out had earlier condemned the chants and called for strong and firm action to be taken.
"The racist chanting heard from some Millwall supporters during yesterday's match is disgusting and typical of mass discriminatory chants that continue to go unpunished," a Kick It Out statement read.
"We reiterate our message: racial hatred - and all forms of discrimination - have no place in society, especially not in 2019. There is no reason why a footballing environment should be the exception to this rule.
"Kick It Out wants to see the relevant authorities take swift, firm and decisive action against the perpetrators.
"We have spoken with the FA, who confirmed they are investigating the incident."
A dramatic 3-2 Millwall win had been overshadowed by a skirmish between Millwall and Everton fans, in which a man was slashed across the face, before the match kicked off.
The Metropolitan Police have yet to make any arrests after footage appeared on social media purporting to show a brawl in the Hawkstone Road area in south east London. A man in his 20s was taken to hospital but his injuries are not life-threatening.