This could be it for Frank Mir.

The former UFC heavyweight champion said Saturday on his Phone Booth Fighting podcast that he would more than likely retire if he is suspended two years by USADA for failing a drug test.

"That was probably my last time fighting," Mir said. ... "I don't see any other way around it. Age is catching up to me now. I'm not gonna get any younger in the next two years."

Mir, 36, said USADA found a small amount of oral turinabol metabolites in his system in an in-competition drug test in relation to his fight with Mark Hunt at UFC Fight Night 85 in Brisbane, Australia. The fight took place March 19 and Mir lost via first-round knockout.

Mir is denying that he knowingly took the anabolic steroid. Oral turinabol's effects include increased strength and endurance. The drug was created in East Germany in the 1960s and involved in the infamous German doping scandal of the 1970s and '80s.

Mir said he passed a Feb. 2 USADA out-of-competition drug test and he does not understand how only a small amount of this banned substance was in his body when he was clean just a few weeks before the bout.

USADA did not immediately respond to a request for comment Saturday morning. The UFC's third-party anti-doping partner typically does not fully comment on cases for the adjudication process is complete. Mir said he has asked USADA to test his B sample.

When talking with his manager Malki Kawa and lawyer, Mir said they asked him how the substance could have entered into his system. Mir said he had no idea and that he really takes very few supplements. The one thing Mir does take is Adderall, but he has a therapeutic usage exemption (TUE) for it. Mir was also a past user of testosterone replacement therapy (TRT), but had a TUE for that as well before it was banned.

"I'm like, 'I have no clue,'" Mir said. "I know that sounds stupid. I'm not an unintelligent individual. I know that if I said I had an injury and I made a mistake, I was tired of being fat, so that's why now I have a six pack, that would be a viable idea. My physique has been such a troubling issue for the last couple of years. I could see me stepping over to the dark side or seeing someone believe that. 'Well, Mir has been fat, he showed up in his last fight with a six-pack. I believe he did it.'"

But that's just not the case, Mir said. For one, he didn't look much different against Hunt than previous fights. He's very confused about what happened and is trying his best to figure out why, so far to no avail.

"Knowledge is just how I am," Mir said. "I like to know things. I'm an inquisitive human being. So not knowing how the molecule ended up in my body is driving me insane."

Mir said he was supposed to work as an analyst for the FOX Sports 1 pre- and post-fight shows this weekend for UFC Fight Night: Dos Santos vs. Rothwell, but got a call Saturday telling him he was pulled. Mir said the UFC rep told him that he would not be able to do any broadcast work for FOX while on suspension, which is a difficult pill to swallow, since Mir is a top-notch analyst and that is another means of making money.

"I'm pretty well-spoken guy, but I don't have a college education," Mir said. "Me making money in other avenues is not going to be as easy as walking into the Octagon."

Over the last 24 hours, Mir said he has been trying to retrace his steps in order to figure out what he took or ate that led to the positive test. He said maybe it could have been something he consumed while in Australia, where he ate some exotic dishes like kangaroo. Mir said he is at a loss and he feels like without something to point to, he could be looking at a lengthy suspension.

Yoel Romero tested positive for a growth hormone secretatogue receptor earlier this year by USADA, but was only given a six-month suspension, because the banned substance came from a tainted supplement. USADA had the supplement tested independently and it came back contaminated. Ibutamoren, the substance Romero popped for, was not written on the label, so the UFC middleweight had no clue he was taking it.

Mir doesn't think he'll be able to present a similarly compelling defense. And he believes that in cases like this, especially when an athlete denies knowingly taking something, it seems to be guilty until proven innocent.

"I know how society is," Mir said. "Every athlete that has ever been popped, if they deny it vehemently it never goes away. It stays on them."

Mir said he is being so open in discussing it and is taking it fairly well, because he knows he's innocent.

"I don't have a guilty conscience," Mir said. "I really didn't do anything. I've competed for 15 years. I've passed every drug test they put in front of me. ... I've never taken PEDs. I don't take them. I don't need them. I've been a pretty big guy my whole life."

The plan is to still fight the sanctions, Mir said. His wife asked him, Mir said, what if USADA extended the ban to something like four years if he kept challenging it? Mir said he would still continue, because he won't own up to something he didn't do.

The unfortunate thing is that Mir isn't sure he'll be able to come close to proving he didn't take anything illegal on purpose. So he is almost resigned to a two-year ban. And that means his career is likely over.

Mir said he could pursue a lifelong dream to be in law enforcement or open a gym. Maybe both. Being away from MMA will give him more time to train with his children and the high-school wrestlers at Bishop Gorman HS that he works out with. Right now, Mir is leaning toward the fact that he'll have to hang up the gloves. The career of one of the great heavyweights in MMA history could be over.

"I'm not a dumb guy," Mir said. "The writing is on the wall. The suspension is already in. The molecule is there."