Scott said the pop stars teamed up to shoot a music video for "Up Out My Face" when Minaj was not yet well-known. He said Carey felt like she was helping Minaj launch her career.
"Mariah went out of her way to be nice to Nicki and make her comfortable," but Minaj was "making faces at her laced with rude comments under her breath," he said.
Scott told TMZ he told Carey how Minaj was acting, but Carey decided not to confront the younger woman and acted as if nothing happened.
A source close to Minaj, whose name was not reported, told TMZ Scott was lying about the 2010 confrontation.
"He works as Mariah's stunt double and of course he would say things like that. He's worked for her for years," the source said.
Auditions for "American Idol" in Charlotte, N.C., were halted for a day after Minaj was heard shouting Tuesday, "I'm gonna knock you out," in an expletive-laden tirade at Carey. Minaj was also recorded calling the multiple Grammy Award winner "her [expletive] highness over there."
Carey was also speaking during the incident, but what she said couldn't be heard.