Manchester United fielded a complaint from Kick It Out on Monday night about a terrace chant a small section of supporters sang about Romelu Lukaku's manhood.
The anti-racism organisation wrote to United after footage emerged of the song, with lyrics describing how well endowed the striker is, during victories over Basle and Everton at Old Trafford.
Kick It Out deem elements of the song - to the tune of Made of Stone by The Stone Roses - 'offensive and discriminatory'.
A spokesman told The Times: "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 it is addressed swiftly."