A spokesperson for Greenhouse reportedly told media: "Nicki was in a car outside, and didn't come in because only a portion of her boyfriend's group of 30 was allowed entry. He was trying to bring in too large a party, and therefore Nicki chose not to come in."
Minaj was recently the subject of controversy after feuding with her fellow American Idol judge and diva Mariah Carey.
She allegedly threatened to shoot Carey and said she was not going to put up with "her f******g highness".
President Barack Obama tried to act as a peacemaker between the two, saying: "I'm all about bringing people together, working for the same cause. I think both outstanding artists are going to be able to make sure that they're moving forward and not going backwards."