Fan footage of the chant, set to the tune of the Stone Roses’ Made of Stone, being sung at United's 3-0 home win over Basel in the UEFA Champions League last week has been shared on social media, and it is believed to have resurfaced in Sunday's 4-0 drubbing of Everton.
Per Paul Hirst of the Times, the lyrics of the song reference the size of Lukaku's manhood and seem to buy in to "the stereotype that black men are better endowed than others."
A Kick It Out spokesman has condemned the chant and said it is discriminatory even if the intention is to express support for the Belgian striker, per Hirst:
"The lyrics used in the chant are offensive and discriminatory. 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."
Hirst added it is believed United will now liaise with Kick It Out and other organisations to address the matter, and a spokesman said there is a "zero- tolerance" attitude to racism at the club.
Per Simon Stone of BBC Sport, there have been no complaints made about the chant to Greater Manchester Police:
Lukaku, 24, moved to Old Trafford from Everton for £75 million in the summer and has made a fantastic start to life under manager Jose Mourinho, netting seven goals in as many games in all competitions.
But it has been made clear by Kick It Out that United's fans need to express their support for him in a different way.
Writing on Red Devils blog The Republik of Mancunia, Scott Patterson was one of the first to enter the debate on the Lukaku chant.
He condemned it as "sub-Jim Davidson drivel that belongs in the 1980s" and urged his fellow United fans to "be better than this."