The Italian football federation (FIGC) launched an inquiry Wednesday after fans allegedly hurled racist abuse at AC Milan midfielder Kevin Constant during a pre-season friendly.
The FIGC "has opened an inquiry into the racist event... in which Milan player Kevin Constant was the target of chants from some of the supporters in the stadium," it said in a statement.
Milan were playing newly-promoted Serie A side Sassuolo on Tuesday when French-born Guinea international Constant appeared to react to racist cat-calls and volleyed the ball into the crowd before storming off the pitch.
The referee warned spectators over the tannoy that the game would be stopped if he heard any racist abuse and substituted Constant with teenage midfielder Mario Piccinocchi. Sassuolo went on to win 2-1.
AC Milan vice-president Adriano Galliani was quoted by Italian media on Wednesday as saying that "racist chants are scandalous, unspeakable, but you cannot leave the pitch. That's not ok."
Constant's reaction echoed AC Milan player Kevin-Prince Boateng's angry exit from the pitch in January following racist insults during a match against lower-division club Pro Patria.
In June, six Pro Patria fans were sentenced to up to two months each in jail for inciting racial hatred.