The Football Association will launch a probe into allegations Millwall fans racially abused Tottenham forward Son Heung-min during Sunday's FA Cup quarter-final.
Chants of "DVD" and "You're selling three for a fiver" were directed at Son, thought to be in reference to the racist stereotype of traders selling bootleg copies of films.
The South Korean delivered a fitting response by scoring a hat-trick as Spurs trashed their League One opponents 6-0. Christian Eriksen, Dele Alli and Vincent Janssen were also on target.
It is now understood the FA will investigate the allegations and are awaiting referee Martin Atkinson's match report, as well as observations from both clubs and the police.
Millwall manager Neil Harris said after the match he had not been aware of the chants but accepted that, if proven, they would represent a blot on his side's excellent run in the competition.
Speaking after the game, Harris said: “I did not hear anything, but me personally, and the club, will not condone that.
“We came here in the right spirit to enjoy an FA Cup quarter-final, so it is detrimental to the club and the competition and it is wrong.
“We want people dealt with harshly, of course, but I think myself and Mauricio [Pochettino, Spurs manager] would rather concentrate on the football.
“For me the focus comes away from what we have achieved in the competition. It is wrong in society and it is wrong in football.”
Millwall are still under investigation by the FA after Leicester complained about their fans' behaviour following their surprise victory in the previous round.
Any punishment for either issue, however, will be considered separately.
There was a heavy police presence outside White Hart Lane ahead of the London derby, with more than a dozen police vans lining Tottenham High Road.
Supporters of both teams had to be separated following skirmishes while bangers, flares and bottles were thrown.
The Metropolitan Police confirmed two people were arrested and charged with public order act offences.