Kiwi UFC middleweight champion Israel Adesanya has addressed the issue with his right pectoral at UFC 253 in Abu Dhabi.
Before his second-round demolition of Paulo Costa, Adesanya's muscle could be seen noticeably drooping, prompting immediate accusations of steroid use from online detractors.
Adesanya has confirmed he'd undergone a blood test and two MRI scans of his pituitary gland to diagnose the swollen "sore" muscle.
He says that the swelling and pain began about eight weeks ago and he'd ignored his girlfriend's advice to see a doctor, preferring to complete the Costa bout first.
"I'll wait for the results," Adesanya tells ESPN. "I might keep you posted or I might let people speculate.
"It’s kind of fun to watch people cry about it."
Adesanya dismisses suggestions of any wrongdoing, claiming his critics are simply trying to undermine his flawless title defence against the Brazilian.
"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 says.
"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."
Gynecomastia - the medical term for enlarged male breasts that can lead to cancer - is often symptomatic of steroid use, but as Adesanya points out, it affects both "boobs", rather than just one.
"Wouldn't it be funny if I died in five months and then it was cancer?" says Adesanya, referring to Black Panther actor Chadwick Boseman's tragic death in August.
"It wouldn’t be funny."
During the post-fight press conference, a reporter asked Adesanya whether there was something medically amiss, only to be quickly dismissed by the 31-year-old.
"Why are you looking at my titties?" Adesanya replied quizzically.
Adesanya vehemently denies he's ever used performance-enhancing substances and his record speaks for itself.
Since he joined the UFC in February 2018, he's been tested 32 times by the US Anti-Doping Agency (USADA) 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," says Adesanya.
"You see, 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 not me.
"Skills, bro. Skills pay the bills."
On the flipside, Adesanya maintains his pre-fight stance that his vanquished opponent Costa will ultimately be exposed for anti-doping.
"You wait until Paulo pops," he says. "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."