Red Star Belgrade have issued a statement apologising for racial abuse directed toward AC Milan forward Zlatan Ibrahimovic during their Europa League match on Thursday.
Ibrahimovic was on the bench but did not play in the last-32 first leg, which ended in a 2-2 draw in Belgrade.
But cameras picked up a fan yelling ethnic insults at Ibrahimovic, who has roots in Bosnia.
What did Red Star say?
In a statement, the Serbian outfit said: "Red Star vehemently condemns abusive chants to Zlatan Ibrahimovic during the Europa League match with AC Milan.
"The club did everything in its power to organise the event on a high level and we will not allow a primitive individual to stain Serbia's traditional hospitality.
"We will work with the authorities to identify the offender and we will also insist that he is punished to the full extent of the law.
"Red Star again sincerely apologises to Zlatan Ibrahimovic and we stress that the club will have zero tolerance for such outbursts in the future."
Why was Ibrahimovic abused?
The striker was born in Sweden to a Croatian Catholic mother and a Bosnian Muslim father.
The fan who abused Ibrahimovic used a pejorative term for Bosnian Muslims, with Ibrahimovic shown on the video to not react to the fan's abusive comments.
The countries that are now Serbia, Croatia, and Bosnia and Herzegovina, among others, were at one point all part of Yugoslavia before the country's breakup in the early 1990s.
The early 1990s also saw a bloody war involving several countries from the former Yugoslavia, which much of the region's population vividly remembers.