Undefeated former welterweight boxing champion suggests his UFC rival is overweight.
WATCH: Conor McGregor vows to 'crumble' Floyd Mayweather
Floyd Mayweather and Conor McGregor traded verbal jabs on Tuesday as the circus-like countdown to their money-spinning superfight cranked into overdrive on the Las Vegas Strip.
Thousands of fans including a sizeable contingent of Irish supporters thronged the heart of the Nevada boxing capital to greet Mayweather and McGregor at their separate grand arrival ceremonies.
Mayweather, the 40-year-old undefeated former welterweight boxing champion, has been lured out of retirement to face McGregor, a star of mixed martial arts' Ultimate Fighting Championship.
The two men meet in a 12-round contest under boxing rules on Saturday that is tipped to become the richest fight in history.
The cross-combat collision has appalled boxing purists, with many decrying the event as a farcical publicity stunt more in keeping with the choreographed traditions of WWE wrestling.
Mayweather and McGregor - who clashed repeatedly during an expletive-laden world media tour to drum up interest for the fight last month - insist however that they are ready to deliver a battle for the ages.
McGregor, a massive underdog in what will be his first professional boxing fight, insisted on Tuesday he was ready to create an upset.
"This is not even close to my toughest challenge ever. I will crumble him," McGregor said.
"I have adapted perfectly to boxing, I am very pleased and ready. I'm a special man, I will prove that August 26, this will go one or two rounds, maybe I will bang him out and hurt him.
"If he survives, I will decide whether I embarrass or seriously hurt him.
"I'm calm and cool, same as I am in every fight. I'm fit, sharp and I'm gonna be ruthless in there. I believe he'll be unconscious inside one round."
McGregor and Mayweather passed each other after their separate introductions, with McGregor taunting the American with a shout of "Why didn't you want to face off?" - triggering a melee between their two entourages.
A relaxed-looking Mayweather meanwhile had earlier insisted the fight would finish inside 12 rounds.
"I talked to you before and said that this fight wouldn't go the distance," Mayweather said. "If you're going to bet, bet it won't go [the distance]."
Mayweather did his best to play down his status as a heavy favourite, insisting that his two-year layoff from the ring had blunted his prowess.
"That's what makes this fight so intriguing, I've been out a few years, feel like I've lost a few steps," Mayweather said. "So we'll just have to wait and see."
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Earlier on Tuesday, Mayweather had taunted McGregor over his fitness, telling the US website FightHype that he believed his opponent would struggle to make the 154-pound (70kg) limit for Saturday's bout.
"Conor McGregor is extremely heavy right now," Mayweather said. "I think he's 164 so he's still got 10 pounds to go."
McGregor hit back at Mayweather's comments.
"He needs to shut his mouth," McGregor said. "It is a fool of a thing. Let him keep praying, praying for weight, for fatigue, praying for me to take a backward step. All he is doing is praying, but he is praying to the new god of boxing."
McGregor could face a painful financial penalty if he is unable to tip the scales inside the limit. Boxers often have the option of cancelling a fight or collecting a larger share of the purse if an opponent fails to make weight.
Estimates vary but some projections indicate Mayweather could make as much as US$200 million (Dh734m) from Saturday's contest, with McGregor collecting around $100m.
Mayweather has fought at 154 pounds before but is more used to fighting at welterweight (150 pounds). McGregor however has fought at 170 pounds in MMA.
McGregor, 29, last week insisted he was in peak condition following a gruelling training camp that had taken him to "hell and back" and left him primed to face either a long or short fight.
"There is no way in hell that I'm not ready to fight in the deepest of trenches in this contest," McGregor said. "We are ready for both scenarios. I'm ready to go to war for 12 rounds and I'm ready to put him away early on."