He said: "I have not seen a man beat a woman like that since Chris Brown beat Rihanna."
"That is a lying, sick, sociopathic, disgusting freak," Mitrione said. "And I mean that. Because you lied on your license to beat up women. That's disgusting. You should be embarrassed yourself."
Fox is the first MMA competitor to go on record about being transgender.
"The reaction has been positive," the 37-year-old said in a March CNN story. "It's just some people, some of society doesn't get it yet. And this is what we're trying to do now, is to inform people and let them know about transgender athletes."
UFC, or Ultimate Fighting Championship, a mixed martial arts promotion group, released a statement about Mitrione's comments.
"The UFC was appalled by the transphobic comments made by heavyweight Matt Mitrione today (Monday) in an interview on the 'MMA Hour,' " the release said. "The organization finds Mr. Mitrione's comments offensive and wholly unacceptable and -- as a direct result of this significant breach of the UFC's code of conduct -- Mr. Mitrione's UFC contract has been suspended and the incident is being investigated.
"The UFC is a friend and ally of the LGBT community, and expects and requires all 450 of its athletes to treat others with dignity and respect."