Napoli defender Kalidou Koulibaly has alleged he was racially abused by Fiorentina fans in Sunday's Serie A match between the teams.
The 30-year-old Senegal international said in a social media post he had been called a "fucking monkey."
"These people have nothing to do with sport," he said. "They must be identified and kept out of the stadiums: forever."
Fiorentina said police were reviewing video footage from the game to identify those responsible.
Koulibaly received support from within Italian football, including AC Milan - who are second behind table-topping Napoli - who tweeted: "There's no place for racism in football, in society, anywhere."
The Italian football federation (FIGC) has received a report on the incident from its match attendee and after talks with Koulibaly will open an investigation.