The New York Post quoted an unidentified witness who said Blige's punch drew blood before the singer and her husband of six years were separated by members of their entourage Tuesday night.
"She turned to him and was screaming, 'You're not going to ruin my night,'" the insider told the Post. "They got up in each other's faces before someone tried to separate them, at which point she shoved the guy aside, pulled back and popped (Isaacs) in the face. ... She was yelling at him, 'What are you gonna do, Chris Brown me?' Four of her bodyguards and two of the club's kept them apart."
Isaacs reportedly was persuaded to leave the Manhattan club where they had been partying with the likes of Jay-Z and Beyonce. Blige is said to have departed soon after he left.
Contacted by the Post, Blige's publicist downplayed the alleged incident.
"People lie and don't know what they're talking about," the representative said.