Manchester United fans sang the controversial Romelu Lukaku chant during their Premier League clash with Southampton in defiance of pleas to refrain from doing so.
A number of the away supporters were heard singing the song - which has been deemed "offensive" by anti-discrimination group Kick It Out - after Lukaku put their side ahead in the first half at St Mary's Stadium on Saturday.
They followed it with a chorus of "we're Man United, we'll sing what we want".
The Belgium international himself called for fans not to sing it after Kick It Out threatened to report perpetrators to the Football Association.
"The lyrics used in the chant are offensive and discriminatory," the group said in a statement given to Omnisport. "Racist stereotypes are never acceptable in football or wider society, irrespective of any intention to show support for a player.
"We have contacted Manchester United regarding the issue and will be working closely with them and The FA to ensure that it is addressed swiftly. If we receive any reports relating to the discriminatory chant, those will be passed on to the governing body and the perpetrators can expect to face punishment."
United stated via their official Twitter account this week: "We remind fans of our commitment to ensuring Old Trafford remains inclusive for all. Action will be taken against any offensive behaviour."
Lukaku issued a similar message to supporters, saying: "Great backing since I joined MUFC. Fans have meant well with their songs but let's move on together."