Los Angeles - Floyd Mayweather believes Conor McGregor is struggling to make the weight for their cross-combat showdown as the final countdown to the superfight cranked into overdrive on Tuesday.
In comments to US website FightHype, Mayweather said he thought Irish mixed martial arts star McGregor looked "extremely heavy" and doubted he would make the 154-pound limit for Saturday's fight.
"Conor McGregor is extremely heavy right now," Mayweather said. "I think he's 164 so he's still got 10 pounds to go."
Former welterweight champion Mayweather is coming out of retirement to face McGregor in a one-off meeting between two of the best known fighters in boxing and mixed martial arts.
Saturday's fight at the T-Mobile Arena is a boxing contest, a fact that will see the undefeated Mayweather start as an overwhelming favourite to claim his 50th straight victory.
UFC champion McGregor, who has never boxed professionally, has vowed to knock out Mayweather inside two rounds.
However the Irishman could face a painful financial penalty if he is unable to tip the scales inside the 154-pound 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.
Mayweather, who is expected to earn at least $100 million from Saturday's contest, indicated he would take the money.
"I get that extra money if you can't make the weight," Mayweather said. "Get those extra millions ready. UFC get those extra millions ready.
"You got to get that weight down like a true champion. A true champion is disciplined and very responsible but we'll see.
"If he don't make the weight, we still going to fight but there's going to be a heavy fine."
Mayweather has fought at 154 pounds before but is more used to fighting at welterweight (150 pounds). McGregor however has fought at 170lbs 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."