Khabib Nurmagomedov has shared an X-ray showing his foot was broken just weeks before he took on Justin Gaethje.
Nurmagomedov suffered the injury in his training camp but refused to pull out of the fight.
He went on to submit Gaethje in the second round to retain his lightweight title before announcing his retirement.
It was UFC president Dana White who revealed the champion had suffered the injuries.
"I think he has two broken toes and a bone in his foot broken, that’s what his corner told me.
"He never told anyone, was just walking around as normal, he is one of the toughest human beings on the planet.
"He is the No1 pound-for-pound fighter in the world and you have to start talking about him having GOAT status with whoever else you think is the GOAT.
"When guys want to fight, the fight and when they don’t they don’t.
"You have got to give them time and let them heal mentally more than physically, with what he has gone through losing his father.
"We are all lucky to have seen him on Saturday night."
Nurmagomedov's coach Javier Mendez later admitted the training camp had been the worst of his charge's career.
"This was the worst camp we’ve ever had in the sense of preparation," he told Yahoo. "Accommodations were the best ever; hospitality was the best ever but we had so much bad luck.
"There was Staph infection with a lot of the guys and the mumps. Khabib had the mumps two weeks going into [camp] and I was like, ‘Oh my God. I’m so concerned.’ He trained one week really light and then the following week he broke his toe next to the pinky toe.
"Because of the broken toe, we were again out. This was a very hard camp but Khabib said, 'Coach, my toe may be broken but my mind is not.' I said I know, and that’s when I knew he was going to fight through all of this adversity no matter what."
