Millwall fans who targeted Tottenham forward Son Heung-min with racist chants should be dealt with strongly, says Lions boss Neil Harris.
South Korea international Son was subjected to chants of "DVD" and "he's selling three for a fiver" during Sunday's FA Cup sixth round tie.
The chants seem to refer to a racist stereotype of Asians as traders selling bootleg copies of films door to door.
"It's a shame to be talking about this," added Harris.
Son scored a hat-trick as Spurs beat League One Millwall 6-0 to reach the FA Cup semi-finals.