Conor McGregor said he regretted his actions in a statement after a brief court appearance over his alleged attack on a busload of fellow fighters.
The UFC star's lawyers said he was still working on a plea deal and Judge Raymond Rodiguez set a new court date of July 26 in a hearing that lasted just a couple of minutes.
McGregor looked serious as he walked into Kings County Criminal Court in Brooklyn, New York, wearing a dark blue suit, white shirt and striped tie.
Mixed martial arts fighter Cian Cowley, who has also been charged over the incident, also wore a dark blue suit for the hearing.
The pair spoke little as assistant district attorney Janet Gleeson said the case had not been presented to a grand jury for possible indictment because of the ongoing plea negotiations.
In a statement he read to a media scrum outside court before departing in a black SUV, McGregor said: "I regret my actions that led me here today. I understand the seriousness of this matter and I'm hopeful that it gets resolved soon."
One fan outside court held up a sign that read: "The champ does what the fook he wants."
The 29-year-old is due to meet with UFC president Dana White to discuss his next fight on June 18.
McGregor left Ireland on Tuesday to head to the United States to face charges over his alleged attack on a bus filled with fellow mixed-martial arts fighters in April.
He and his associates were filmed "storming the building", smashing windows and throwing a chair and a metal guard rail at the bus parked at New York's Barclays Centre for the UFC 223 fight.
"The Notorious" faced court at Brooklyn Criminal Court at 10am local time (12am AEST) and could face seven years' jail if found guilty over the alleged wild attack.
McGregor posted an Instagram photo on Tuesday of himself with son Conor Jr and MMA fighter Cowley as he prepared to fly out of Dublin Airport on a corporate jet.
He also shared a post of himself with Cowley that appeared to reference the court appearance with the caption, "from the cells to the stadiums. Not a scratch. They done nothing. Jet leaves Tuesday my brother."
Both men turned themselves in to police after the incident outside a UFC news conference on Thursday, April 5, before McGregor was released on $65,000 bail and Cowley on $30,000.
"He's the most visible face on the planet. He has no criminal history and the bail package is completely appropriate," McGregor's lawyer Jim Walden told the court.
Two athletes were injured by flying glass in the clash and McGregor was caught on CCTV repeatedly punching a security guard, the Brooklyn Court heard at his arraignment.
Lightweight Michael Chiesa was hospitalised and treated for cuts to his face and flyweight Raymond Borg was left with multiple corneal abrasions. Both their fights that Saturday were cancelled. "I'm devastated to say the least," tweeted Chiesa.
UFC vice-president of athlete development Reed Harris, who was on the bus, tweeted after the incident: "We thought we were gonna die."
Harris, who later deleted the post, added: "I've been in dozens of scuffles in UFC. Never once was I scared.
"This time was different."
Just 24 hours earlier, White had said "it would be awesome if Conor McGregor was here", but he did not believe the Irishman had any plans to attend.
White said afterwards that McGregor had "loaded up the plane full of guys from Ireland" and co-ordinated an attack that was "the most disgusting thing that has ever happened in the history of the company."
The meltdown reportedly came after McGregor heard of the UFC's decision to strip him of his lightweight title and award it to Khabib Nurmagomedov due to inactivity.
The Irishman tweeted that morning: "You's'll strip me of nothing you's do nothing c**ts."
The fighter reportedly decided to travel to New York to defend his friend Artem Lobov — who was also present for the incident — after he had clashed with Nurmagomedov in a hotel lobby in the city days earlier.
The Irishman has now been on an almost 19-month hiatus, but White revealed at the weekend that his next opponent will be lightweight champion Nurmagomedov.
McGregor faces a string of charges including three counts of misdemeanor assault, one count of felony criminal mischief, attempted assault, menacing and reckless endangerment.
Cowley, 25, was also charged with felony criminal mischief. "It was nothing," the younger man told Metro. "We'll just get it out of the way and then get back to work.
"Well, I have been working anyway. It was nothing, it was all blown up. That's not even in my head anyway."
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