Arsenal have started an investigation after a social media video appeared to show a fan racially abusing Napoli defender Kalidou Koulibaly during the Europa League quarter-final.
The incident occurred during the Premier League side’s 2-0 win in Thursday’s first leg at the Emirates Stadium.
“We utterly condemn use of this type of racist language and have launched an investigation to identify the culprit,” the club said in a statement on Friday.
“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 Emirates Stadium.”
The north London club urged fans to be vigilant and report any such problems with racism directly.
Recent high-profile incidents, including monkey chants aimed at England players during a Euro 2020 qualifier away to Montenegro and in the domestic game, have again highlighted the lingering problems within football.
On Thursday, Chelsea barred three supporters from attending their Europa League quarter-final first-leg clash at Slavia Prague after a video was circulated on social media containing racist abuse aimed at Liverpool forward Mohamed Salah.
Manchester City and England forward Raheem Sterling has used his position to speak out against racism, as well as making defiant gestures on the pitch with goal celebrations and posting messages on social media.