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Nate Diaz's coach, Richard Perez, has described Conor McGregor's weight gain as "shady" and accused the Irishman of being on steroids ahead of UFC 196.

The current UFC featherweight champion was supposed to move up a weight division for UFC 196 to take on Rafael dos Anjos for the lightweight title, but the Brazilian pulled out last week due to injury.

Diaz has stepped into the breach for the March 5 Las Vegas event, but he and McGregor will fight at welterweight—two divisions up from the the Dubliner's last fight.

And Perez has echoed Diaz's accusations that the ease with which McGregor has added pounds suggests he is on steroids, per Submission Radio (via Bloody Elbow's Anton Tabuena):

I sure do believe that [he's on steroids], heck yeah. Some guys, they get busted - and to be honest with you, I know McGregor has got to be on some kind of steroids. He’s pretty big, and then all of a sudden [he’s] jumping to 170? Yeah there’s no way, because I mean, he was supposed to be fighting at 155. So if you think about it, he was focusing on training at 155. He only had two weeks to go. And all of a sudden he’s gonna jump to 170? So no, there’s something going on. When Nathan mentioned it to him, he got defensive, he got angry. If somebody would have told me that I was fighting and he told me, you know, steroids, I would laugh and say, "yeah give me some more steroids, heck yeah, ah ha sure." But he got defensive and mad, you know, "I’m not on steroids, I’m not on steroids!" You know, he was like trying to defend himself. So that, just his actions and the way he talked, there’s something behind that.

Listen to the full interview below:

Perez added Diaz was "ready" to fight at 155 pounds but said he did not think McGregor could have made that weight, which was "shady," considering he was supposed to take on Dos Anjos at lightweight.

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However, previous reports had suggested the reason for the fight taking place at welterweight is because Diaz could not have cut down in such a short space of time, per Sky Sports' James Dielhenn.

Whatever the situation, there is clearly some bad blood between the two sides ahead of Saturday's fight, and the pre-fight press conference was a typically combative occasion, per the UFC (warning: clip contains NSFW language):

Diaz, 30, is traditionally a lightweight and is currently the UFC's fifth-ranked fighter in the division.

His last outing was a unanimous-decision victory over Michael Johnson at the end of last year, his first fight after his defeat to Dos Anjos.

Meanwhile, McGregor stretched his unbeaten UFC record to seven fights with a 13-second knockout of Jose Aldo in December, per BT Sport:

The 27-year-old is undoubtedly one of the UFC's biggest stars, and defeating Diaz at welterweight would be a significant victory as McGregor looks to dominate multiple divisions—he took the Dos Anjos fight in an attempt to become the first fighter to hold two world titles at the same time.

However, if Diaz and Perez's accusations about steroid use are ever revealed to be true, it would be a huge blow for the UFC, given McGregor's status in the sport.