The Serie A season hasn't even started but Italian football is already back in the racism spotlight. 

The Italian football federation launched an investigation on Wednesday after AC Milan midfielder Kevin Constant walked off the field following racist abuse during a friendly match.

The incident took place on Tuesday during a 2-1 friendly loss to home side Sassuolo in the Trofeo TIM tournament, which also involved Serie A champion Juventus.

Constant, who is black, walked off the field after kicking the ball into the stands in the 34th minute, emulating the actions of Kevin-Prince Boateng last season.

The referee allowed a substitute to come on and also ordered an announcement warning that the game would be suspended if further incidents occurred.

Following racist abuse during a friendly in January against Pro Patria, Boateng also kicked the ball at a section of the crowd before walking off the field with the rest of the Milan team.

Milan has not commented on the incident but shortly afterward Constant tweeted a mock-up movie poster of teammates Boateng, Mario Balotelli and M'Baye Niang and the title 'Stop Racism.'

Sassuolo is about to start their first ever season in Serie A after winning the second division last season.

Source: Al Jazeera and agencies