Pearson (14-6 MMA, 6-3 UFC) told MMAjunkie.com (MMAjunkie.com
) that Sotiropoulos (14-5 MMA, 7-3 UFC) punched his assistant boxing coach off-camera over a Twitter beef between he and the Aussie.
The boxing coach, Erin Beach, then knocked out Sotiropoulos.
"That's why I said I lost all respect for him and that's why I didn't shake his hands afterwards," Pearson said. "That's why I'm not his friend now – because he acted unprofessional."
Beach works out of the Alliance MMA training center in San Diego, where Pearson does his fight camps. He was unreachable for comment.
After knocking Sotiropoulos down several times in the UFC on FX 6 headliner, Pearson cinched his win with a stiff jab that took Sotiropoulos off his feet in the third round.
The two served as opposing coaches on "The Ultimate Fighter: Team Australia vs. Team U.K.," which concluded at the event with the Australians and Brits splitting "TUF" crowns in the lightweight and welterweight divisions.
UFC on FX 6 took place Saturday at Gold Coast Convention Centre in Gold Coast, Australia. The event's main-card aired live on FX while prelims aired on FUEL TV.
Pearson couldn't remember exactly when the incident took place but said it was midway through filming, which, for the six-week filming, means it was in early August.
Pearson said he and Sotiropoulos had been arguing on Twitter, and Beach had inserted himself into the conversation at some point.
Pearson said Sotiropoulos blindsided Beach, who began fighting back. The incident happened "off-camera" on the reality show set in Sydney, he said.
The scrap drew an instant response from UFC President Dana White, who raised Pearson and his team on the phone.
"Dana chewed our heads off," Pearson said. "George was acting unprofessional. I get paid to fight; I don't fight in the streets for free."
While Sotiropoulss' alleged KO would not have fallen within a time frame to preclude him from competing against Pearson, it could have severely affected his preparation if he allowed himself to recover.