Manchester United have asked for CCTV footage to help identify fans who sang a controversial song about striker Romelu Lukaku during Saturday's win at Southampton.
Lukaku, 24, asked fans to "move on" from the chant on Friday.
However, the song was heard in United's 1-0 Premier League victory at St Mary's Stadium.
United said they will "take further action against individuals if this continues".
A statement read: "The club and the player have been clear in asking for an end to the chant.
"The club is in discussion with the police and has asked for CCTV footage from Southampton."
United said they have a "zero-tolerance stance" on offensive chanting and behaviour.
Anti-discrimination group Kick It Out has described the lyrics - about the size of the 24-year-old's penis - as "offensive and discriminatory".
Speaking after the match, United manager Jose Mourinho said he did not understand any of the songs heard at football matches.
He said: "The only music I understand clearly is one of my opponents - not today but in other games - where they tell Mourinho to go to some place.
"The only thing I will say is the support was amazing from the first to the last minute."
A spokesman for Kick it Out said: "Kick It Out would like to reiterate its stance that such behaviour has no place in football.
"Romelu Lukaku himself has requested that the supporters 'move on' from singing the chant in question and Manchester United now has a responsibility to ensure that the request is complied with."
Lukaka scored the only goal at Southampton, his sixth of the season since joining United from Everton for an initial £75m.