Fashion designer Jack McCollough, who was allegedly headbutted by Kiefer Sutherland at a party in lower Manhattan early Tuesday morning, is slamming reports that he provoked the actor.

"Anyone who knows Jack McCollough knows that he would not hurt a fly," a rep for McCollough, of the New York-based fashion empire Proenza Schouler, tells PEOPLE exclusively. "All we can say at this point is that he was the victim of a vicious, violent, unprovoked assault and that the matter is in the hands of the authorities."

One report claims that McCollough bumped into fellow party guest Brooke Shields, prompting Sutherland to get physical with the designer. New York's Daily News reports that McCollough – a friend of Shields's – interrupted her and Sutherland while they were speaking outside the SoHo nightspot SubMercer and that Sutherland then allegedly headbutted McCollough after the two men exchanged words.

But one guest at the event tells PEOPLE that the altercation came as a surprise to bystanders. "Jack walked into the party and tried to order a drink, and then the next thing he knew, he got headbutted for no identifiable reason," the partygoer tells PEOPLE. "Jack did nothing other than walk into a party. He did not bump into Brooke. It's just puzzling.”

According to an NYPD spokesperson, the incident, which occurred around 2 a.m., is under investigation.

Sutherland's lawyer, Blair Berk, had no comment.