European football governing body UEFA said that the correct anti-racism protocol had not been followed during the Italian league game between Inter Milan and Napoli midweek amid repeated abuse of Senegalese defender Kalidou Koulibaly.
Napoli's French-born Koulibaly was targeted by monkey noises and racist chants at the San Siro, before being sent off for sarcastically applauding referee Paolo Mazzoleni.
Three announcements were made over the loudspeaker imploring fans to stop the chants, but they continued.
According to UEFA's protocol, the match should have been suspended then but instead the game was allowed to continue.
In a joint statement UEFA and players' union FIFPro said Friday they were "very concerned by this unacceptable racist incident and by what appears on the surface to be a failure to respect the widely-recognised three-step anti-racism protocol.
"Koulibaly was subject to racist chanting and, despite announcements made by the stadium speaker, the chants did not stop. Moreover, it seems that Napoli's coaching staff had already informed the referee several times of racist chants."
"FIFPro and UEFA support the Italian football authorities on any additional measure that will be taken to tackle racism in stadia for which FIFPro and UEFA have a zero-tolerance policy."