The revelation came after he talked about how poor his preparations were for UFC 158, which ended up a lopsided loss at the hands of champion Georges St-Pierre on Saturday night at the Bell Centre. A reporter then asked him whether he was considering changing fight camps.
"I can't be jumping teams. I just have to invest a little bit more, now that I have a little bit more money," said the 29-year-old from Stockton, Calif. "You know what, I've never paid taxes in my life, I'm probably going to go to jail.
"Nobody wants to hear about that, nobody wants to hear that kind of talk or what's really going on with me," he added after reporters laughed. "I might as well as be a kid. I've had fight after fight after fight after fight. You don't know what that does to somebody that didn't graduate high school? You don't understand."
It was just the latest bizarre utterance from a fighter who declared in the cage after the fight that he has retired, only to join the post-fight news conference midway through to say he wanted a rematch with St-Pierre or possibly Carlos Condit.
Diaz's rambling, sometimes incomprehensible monologues during the pre-fight news conference seemed amusing. After Saturday's loss, they seemed somewhat sad, although UFC president Dana White disputed that view.
"Nick Diaz has been in the game a long time. If you saw his paycheque tonight, you wouldn't feel too sad for him," said White.
"At the end of the day, Nick has been in the sport forever. He wanted a shot at the title, he got a shot at the title and he got paid a lot of money for it. What's sad is he better go pay those taxes, a soon as he gets that cheque. That will be sad. ... somebody better handle that with this cheque and make sure that that kid doesn't end up with nothing."
White said he may speak to Diaz's lawyer to see if he can help.
Asked if there is a future for Diaz in the UFC, White was non-committal.
"We'll see what happens from here on out," he said. "It's not like I don't know what to expect being in business with Nick Diaz.
"Then when he does show up, he does fight."
White said he didn't think Diaz should retire but noted that when a fighter keeps talking about quitting, it's usually time to call it quits.
Diaz also admitted to poor preparation in Montreal, citing the time difference.
"I was so confused," he said. "I needed some kind of coach telling me 'Listen, you're going to have to go to sleep, dude.' Because I was like should I stay up, should I go to sleep?"
He said he slept until 8 p.m. fight night and didn't feel right until he was standing across the cage from St-Pierre.
"I've been a lot more ready for a lot of fights," he said.
While Diaz (27-9-0 with one no contest) seems to constantly have his back up, White says he has never got into real trouble.
Still, he and his entourage clashed with other camps after fights in Strikeforce and he once brawled with Joe Riggs in the Las Vegas hospital they were taken for a checkup after their UFC 57 fight in 2006.
He has also tested positive twice for marijuana, once in Pride and once in the UFC. He served a one-year suspension prior to the GSP fight.
Known for trash-talking in the cage, Diaz did talk a little to GSP during the fight but his hands were full most of the time. And at the end of the third round, he aimed a blow at the champion after the bell rang.
White said Diaz should have been deducted a point for that.
"I was just being really mean out there," said Diaz.