English giants Arsenal have opened an investigation after Napoli defender Kalidou Koulibaly was allegedly racially abused by a fan.
A social media video appeared to show a fan racially abusing the Senegal international during Arsenal's 2-0 win over Italy's Napoli on Thursday night.
The fan who, reportedly used a racial slur in the video, was filmed during UEFA Europa League quarter-final first-leg clash.
"We utterly condemn the use of this type of racist language," a club statement read.
Arsenal stated that they have a "zero-tolerance" approach to racial abuse.
"We have launched an investigation to identify the culprit."
"We operate a zero-tolerance approach and anyone behaving like this is not welcome at Arsenal and will be banned from matches.
"We have an extremely diverse community of fans who are all part of the Arsenal family and such incidents are rare at the Emirates Stadium.
"We encourage supporters to report any incidents as they happen to stewards or via our matchday alert service," another statement.