Israel Adesanya took a blood test and two MRI scans to diagnose a swollen pectoral muscle after his dominant title defence against Paulo Costa at UFC 253.
The Kiwi middleweight, whose swollen pectoral prompted speculation from fans and rivals about steroid use, denied the rumours and revealed the nature of the swelling.
He said he's currently waiting for the results from the scans of his pituitary gland to diagnose the injury.
"I'll wait for the results," Adesanya told ESPN. "I might keep you posted, or I might people speculate. It's kind of fun to watch people cry about it."
Adesanya's critics immediately assumed the worst about his appearance at his title defence on Sunday, where he took out Costa in a second round TKO.
Even his rival, former light heavyweight champion Jon Jones, cast a sideways glance at Adesanya's pectoral before his win over Costa.
At the post-fight press conference, Adesanya brushed off questions about his appearance, saying: "Why are they looking at my titties?"
Now the 31-year-old has offered a full explanation of his appearance, which he says was an injury he carried for eight weeks ahead of his title bout.
His right pectoral started swelling, increasing in size and was "quite sore", but he chose to put off seeking medical attention before one of the biggest fights of his career.
"I don't know what this is, but you know what? With a performance like that, I would think I was on steroids, too," Adesanya said. "They need something. 'It couldn't just be him. It couldn't be him. It must be something'. So for me, it's just fun and games."
Adesanya denies ever using steroids and has been tested 32 times by the US Anti-Doping Agency without issue.
"I'm not one of those people who needs a crutch, that when that gets taken away, they feel weak, they feel inadequate," he continues.
"You see when when USADA came through, a lot of people fell off. A lot of bodies changed, and a lot of people didn't feel good enough without their little magic supplements. But yeah – not me. Skills, bro. Skills pay the bills."
Adesanya admitted that he had to Google the word gynecomastia, the medical term for enlarged male breasts that can be a byproduct of steroid use. He pointed out that the condition linked to steroid use affects both breasts – not just one in his case.
There were no critics, however, after Adesanya's stunning display against Costa as he took apart the Brazillian challenger with ease, eventually stopping him in the second round.
Adesanya also laughed off his opponent's comments after the fight, where Costa promised to avenge the loss and called him "human trash".
"You wait until Paulo pops," he said. "I can't wait. I told you, I'm going to pop him before USADA does. When he pops, ooh, I'm going to gloat."
He also couldn't help but gloat to his detractors once again: "Cry all you want … the bottom line is, I told you so."
Adesanya is currently in managed isolation back in New Zealand after travelling back from Fight Island in Abu Dabhi.