Conor McGregor vows to knock out Nate Diaz inside one round

Featherweight champion Conor McGregor has vowed to knock out replacement opponent Nate Diaz in one round when the pair clash at UFC 196 on March 5.

The 27-year-old Irish star was scheduled to attempt to make UFC history by defeating lightweight champion Rafael dos Anjos and becoming the first fighter to hold titles at two different weight classes at the same time.

But Dos Anjos was forced to pull out of the bout after breaking his foot in training, forcing the UFC to scramble for a replacement opponent.

Featherweight contenders Frankie Edgar and Jose Aldo were contacted but neither was in a position to accept the fight on such short notice - Edgar has a groin injury and Aldo is not in fighting shape.

That prompted the UFC to look to fan favourite Diaz to save what is the company's first marquee fight card of 2016.

The weight the fight would take place was an initial stumbling block as Diaz's camp said he could not cut to lightweight (155lbs) with less than two weeks to prepare.

The UFC asked him to get to a catchweight of 160lbs while Diaz wanted 165lbs. McGregor, who has only ever fought at 145lbs in the UFC, stepped in and said he would fight Diaz at welterweight (170lbs) as he wanted his opponent to be "comfortable".

Speaking at a highly-charged news conference to promote the showdown, McGregor said: "Nate for me was the leading option. There were many, many options but in reality, many people pretended they wanted the fight until the fight actually presented itself.

"Frankie (Edgar) never shut up and then when he was given a phone call and a date, he hasn't been seen or heard since. Jose (Aldo) also. Jose was in camp preparing in case (Rafael) dos Anjos pulled out, and then all of a sudden Dos Anjos pulls out with his bruised foot and Jose is not fit.

"As long as there's an opponent and a date, you'll see me. I love movement and money. And I love the movement of money. The only weight I (care) about is the weight of them cheques, and my cheques are always super-heavyweight."

Diaz, the UFC's number five lightweight contender, who has also fought at welterweight, will have a size advantage over McGregor in the fight but the brash Dubliner is predicting another spectacular knockout.

"I feel that me and Nate, we have a similar will," McGregor said. "But the skill, doesn't match the will, and that's where the difference will be. I feel his repetitive foot patterns and his poor motions are too readable, too predictable.

"He'll be too slow in there. My speed will stifle him. With his soft body and his lack of preparation, he will not be able to handle the ferocity. End of the first, I feel like he will be put away."

McGregor also had some harsh words for his previously scheduled opponent Dos Anjos.

"Dos Anjos has a bruise on his foot. Did ya see it?" McGregor said. "t's a bruise. Ice. Ibuprofen. If I jumped under an X-ray, the doctor would slap me and say: 'What are you doing, kid? Get out of here! Stop this."

The most contentious exchange of the heated conference came when Diaz accused the entire UFC roster of being on steroids and included McGregor - who has always been a staunch critic of any fighters found guilty of steroid use - in his outburst.

"Everybody is on steroids," Diaz said. "The whole UFC. Everybody. You and (Rafael) dos Anjos and (Anthony) Pettis and everybody."

That prompted the typically composed McGregor to lose his cool as he stood up and started yelling at Diaz before sitting down and reminding the Californian that two of his Skrap Pack team-mates, Jake Shields and Gilbert Melendez, have been found guilty of using performance-enhancing drugs.

"I'm not on no steroids," McGregor said. "Don't be bringing my name up with that. What are you talking about? Your two teammates were on steroids. Your two boys. The Skrap Pack. Remember that? Did you know they were taking that stuff?"

That exchange sent UFC president Dana White into damage-control mode and he was soon on record with TMZ.com, reminding the world of the stringent anti-doping programme the UFC has introduced in recent months.

"The UFC unquestionably has the best drug-testing programme in all of sports," White told TMZ. "All done by the United States Anti-Doping Association."

Diaz, for his part, appears confident he can handle McGregor's explosive punching power and become the first man to defeat him inside the Octagon.

"Yeah, I'm just going to kill or be killed," the former lightweight championship contender said of his tactics for the fight. "That's what I'm coming with."