The 'Beauty and a Beat' singer allegedly 'went nuts' at a fellow reveller as he partied at hotspot South Pointe, in ritzy New York resort the Hamptons, leading to a physical altercation between members of the star's entourage and club patrons.
The fight is thought to have been triggered by a heated exchange between Justin, 19, and a male club-goer after a female friend attempted to hit on the singer in his roped-off V.I.P. section.
Altercation: Justin Bieber, pictured in a July Instagram image, allegedly stripped off his T-shirt in a New York nightclub and 'went nuts' at a fellow revellerA source told the New York Daily News: 'He ripped his shirt off and went nuts. He was screaming.'
Justin's security team quickly intervened and took the star out to the club's car park to cool off, but according to TMZ things flared up again.
Justin - who was by then sitting in his SUV - allegedly jumped through the sunroof onto the hood of the car. At that point it's unclear what happened, but the alleged victim was knocked out on the cement.
Police confirmed to TMZ Justin's entourage went after the clubgoer, after he had become aggressive with them.
A spokesman for Bieber confirmed to MailOnline: 'Justin was not involved in any altercation.'
Bieber's entourage are now under investigation after a nightclub patron was left sprawled out in the parking lot and taken to a hospital.
Spitting: Justin Bieber was pictured hurling saliva over a sea of waiting fans from his hotel balcony in Toronto
More antics: The singer grins as he points down at the unfortunate fans he sprayedAn investigation is underway after the alleged victim filed a police report. Justin will not be the target of the investigation.
Earlier in the evening, the 'Boyfriend' hitmaker's bodyguards were accused of being 'heavy-handed' with fans who had hoped to meet the star.
Justin arrived with his entourage and four bodyguards at around 2am and quickly 'took over' the V.I.P. area, which was closely guarded by his eagle-eyed minders.
The security team were described as being 'intimidating' and 'overbearing', and even flashed a torch in the face of partygoers who tried to snap pictures of Justin on their cameraphones.
It comes after a string of incidents where Bieber demonstrated 'pop brat' behaviour'.
He has been pictured spitting on fans and urinating in a janitor's mop bucket in the kitchen of a New York night club.
Even the star's mother struggles to justify some of his behaviour.
Back to work: Bieber appeared tired as he performed at the Prudential Center in New Jersey on Thursday night
Screaming fans: His recent scandals didn't stop the adoring masses from trying to grab hold of Justin as he danced down the stage'I'm not naive to think that my child is perfect and making all the best decisions of his life,' said Pattie Mallette, who is only 38-years-old herself.
While appearing on the Bravo show, Watch What Happens Live, Mallette went on to say: 'He knows what I disagree with and he knows all the things that I'm really proud of him for, too.
'I mean, people don't talk about all the great things he does every day,' she told host Andy Cohen when appearing with another celebrity parent, Kris Jenner.
'Every night before a show, he meets with Make-a-Wish kids. He goes to sick kids' hospitals. He visits with them (and) takes his time. He gives back to charities.'
Parenthood trauma: Justin Bieber's mother, Pattie Mallette stuck up for her son following recent scandals
