It says the lyrics, about the size of the 24-year-old striker's penis, are "offensive and discriminatory".
"Racist stereotypes are never acceptable, irrespective of any intention to show support for a player," said Kick It Out.
Manchester United say they will liaise with Kick it Out on the matter.
The Old Trafford club are also waiting to learn whether the chant about the Belgium forward is regarded as racist for criminal purposes and is therefore actionable.
A United blog has already asked the club's fans to refrain from the song.