A photographer reportedly saw a steward retrieving a banana and heard monkey chants directed at Italy striker Mario Balotelli.
A Uefa spokesperson said: “We are looking into the reports.”
Alleged racist chanting in the Spain-Italy and Russia-Czech Republic games are already subject to investigations.
A Spanish fans’ group has said some of its country’s supporters abused Balotelli in their game with Italy, while Czech Republic defender Theodor Gebre Selassie told reporters he “noticed” racist chants directed at him.
Balotelli, who started the 1-1 draw against Croatia, said before Euro 2012 that he would “not accept racism at all” and would walk off the pitch if racially abused by fans.
More security at open training sessions
Uefa has asked local authorities to step up security for open training sessions at Euro 2012.
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The request follows the racial abuse of Dutch players by some spectators watching training in Krakow last week.
An increased police presence at training grounds is one option that Uefa have asked to be considered.
“Any such behaviour is totally incompatible with Uefa’s zero-tolerance policy,” a statement said.