Ghanaian midfielder Alfred Duncan was the subject of racist chants during Sassuolo's 2-2 draw with SS Napoli. Duncan was yellow-carded in the 88th minute, four minutes after Arkadiusz Milik had equalised for Napoli.
He was racially abused by Napoli fans who monkey howled whenever he received the ball.
Milik scored his first goal since his lengthy injury layoff but it wasn't enough to prevent Napoli from drawing 2-2 at Sassuolo on Sunday and missing the chance to move second in Serie A.
Milik scored three minutes after coming off the bench to rescue a point for Napoli and move it to within one-point of second-placed Roma, which visits bottom club Pescara on Monday.
Second spot in Serie A secures automatic entry into the Champions League group stage, while the team that finishes third has to go through a playoff.
After an even first half, Napoli broke the deadlock seven minutes after the break thanks to a rare header from Dries Mertens. It was the diminutive Belgian's 22nd league goal of the season — as many as he had scored in total in his three previous seasons at Napoli.
However, Napoli gifted Sassuolo the equalizer seven minutes later as Marek Hamsik's terrible headed backpass to Pepe Reina was intercepted by Domenico Berardi, who fired home from close range.
Mertens almost immediately restored his side's lead but saw his free kick come off the crossbar, while a Lorenzo Insigne effort also hit the inside of the post for Napoli.
Sassuolo took the lead 10 minutes from time following a fantastic save from Reina to deny former Napoli hero Paolo Cannavaro, but Antonino Ragusa hooked the ball back in from the byline for Luca Mazzitelli to drive into the bottom right corner.
Milik was brought on in the 82nd and leveled two minutes later. A Jose Callejon corner was knocked down by Raul Albiol and the Poland international spun to fire in from close range for his first goal since he was injured on World Cup duty in October.
AC Milan was playing Empoli in the pick of the afternoon matches, while Serie A leader Juventus hosts Genoa later.