The Football Association (FA) are to investigate alleged racist chants towards Tottenham's Son Heung-Min by Millwall fans.
The alleged chants are thought to include taunts of "DVD" and "he's selling three for a fiver". The chants seem to refer to a racist stereotype of Asians as traders selling bootleg copies of films door to door.
Millwall manager Neil Harris said fans found guilty should be dealt with "harshly".
"It's a shame to be talking about this," added Harris "I didn't hear anything but myself and the club won't condone that if there is. I'm sure it will be investigated and left to the authorities.
"We want people dealt with harshly of course. It's wrong in society and wrong in football."
Tottenham have said any footage that could help catch those behind the alleged racism would be passed on
A Tottenham spokesperson said: "We strongly condemn the use of any racist language."
Millwall are still being investigated by the FA after Leicester complained about the behaviour of the Millwall fans following their victory in the previous round.
Millwall have said: "Millwall have led the way on anti-discrimination initiatives and will continue to do so. The club is assisting the FA with its investigation and will make no further comment until that process is complete."