The duo were celebrating the start of 2013 at Miami bar Story but ended up arguing with each other, supposedly over Vergara's former relationship with club owner Chris Paciello, the New York Post reports.
The situation escalated when Loeb became involved in a row with a fellow reveller, a source claimed.
"In the early hours, Nick and Sofia were arguing before he got into a dispute with somebody at a neighboring table," the insider alleged. "Some pushing and shoving started.
"Sofia stepped in to try to calm the situation, but somehow she ended up getting pushed and shoved also. Her strapless dress was torn or pulled down in the melee, exposing her cleavage in front of other people and her son Manolo, who was so offended he left the club. It was crazy."
The source claimed that Loeb was then removed from the nightclub and was followed by Vergara, with the couple reportedly making amends outside.
"Things got pretty heated, but [Vergara] was never hit," the insider said. "Nick was pretty bruised from struggling with security. None of the drama was Sofia's fault, but despite the big scene [Loeb] created, they made up outside the club and she took him back to their hotel."
Vergara and Loeb reportedly split in May but then reunited a month later, and the couple confirmed their engagement in August.