"We utterly condemn the use of any racist language and have launched an investigation to identify the culprit," an Arsenal spokesman said.
"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."
Koulibaly has become a symbol of the battle against racism in Italian soccer since being subjected to racist insults from some Inter Milan fans during a Serie A match in December.
Elsewhere on Thursday, three Chelsea fans were stopped from entering Slavia Prague's stadium for their Europa League game after an alleged racist chant about Liverpool's Egyptian striker Mohamed Salah circulated on social media.
(Reporting by Shrivathsa Sridhar in Bengaluru, editing by Pritha Sarkar)
