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"Some boys surrounding the field made some offensive chants towards Mario Balotelli and one of them pronounced a racial insult," the Italian soccer federation said in a statement.
The fan called him a "black piece of s***," the Guardian reports.
According to Gazzetta dello Sport, Balotelli told his teammates, "It's incredible, these things happen only in Rome and Florence."
Balotelli, an Italian of African descent, has been the target of racial abuse in Italy since a young age. At a 2010 game against Romania, fans unfurled a banner that said, "No to a multiethnic national team." In each of the past two seasons, Inter Milan - the rival of Balotelli's club AC Milan - has been fined for racial abuse directed at Balotelli.
During Euro 2012, Gazzetta dello Sport published a racist cartoon depicting Balotelli has King Kong on Big Ben before the Italy-England game. When he hugged his adopted mother after the match, the photo went viral.
After an up-and-down season for Milan, Balotelli is expected to play a key role for Italy in Brazil.