Butler was traded Thursday during the 2017 NBA Draft from the Bulls to the Minnesota Timberwolves.
After news of the move broke, Travelle Gaines compared Forman to a drug dealer.
Butler and Gaines were both in France for fashion week when the trade went down. Gaines has a photo of himself with Butler as his Twitter profile photo.
"I completely disagree when someone takes a shot like that," Bulls executive vice president John Paxson said, referring to the tweet, at a press conference. "It's not right. It's not professional. And he shouldn't have done it. I've worked with Gar for a long time and it's an unfair characterization. He has motivation. Maybe he is emotional, but we are in a position where we have to do what we feel is right."
"If he's unhappy, that's on him, not on us."
Butler called Gaines "my trainer, my guy" in an interview with the Chicago Sun-Times.
"I don't control what he says,'' Butler told the Sun-Times. "He's his own person. We'll talk about it [afterward] obviously, but I don't control what he says on social media. That's his. There's no right in me to tell him what he can or cannot do.
"[His message] doesn't say much about [my feelings]. That's Travelle Gaines. He's my trainer, my guy, and you can say what you want to say about it, but [that tweet] has very little to do with me to tell you the truth. Yes, I know what he said. Yes, I saw it, but that's his take on it. I didn't say that. I didn't post anything like that.''
Butler also thanked the Bulls for picking him in the 2011 NBA Draft.
He wrote a goodbye ode to his fans on Friday.
Butler's former Bulls teammate and fellow Marquette Golden Eagles alum Dwyane Wade was a bit less pointed in his displeasure about the trade.
"D.A.M.N haha. My Guy!!! #Morelife," Wade wrote on social media as a caption for a photo of himself and Butler laughing.
Forman told the high road in an interview Friday following Butler's departure.
"Jimmy gave us so much, to this organization to this team," Forman told the Bulls website. "He was great in this community. Obviously he was a terrific, terrific player, and you hate to see him go, but it was obviously a move we felt we needed to make in order to kind of jumpstart where we're at and give us direction as far as a rebuild is concerned."