Chael Sonnen believes Conor McGregor is making a mistake fighting Donald Cerrone at welterweight over five rounds.
The Notorious faces Cowboy on January 18 in what will be his first UFC bout in over 15 months.
The Dubliner will fight at 170lb for just the third time having previously won and lost fights at the weight against Nate Diaz.
And Sonnen believes he may pay the price for doing so over five rounds as the main event at the T-Mobile Arena in Las Vegas.
"One thing I thought got a little lost was that this is happening at welterweight and I think that is significant," the former UFC title challenger told ESPN.
"As soon as that came out the line in Vegas dropped from Conor McGregor being a 1/5 favourite to a 1/2.5 favourite.
"At 170lb, Conor is batting at 50 per cent; he's fought there twice, won once and lost once, both against Nate Diaz.
"Conor McGregor, who is striking-heavy and not known for ground-and-pound or submission, has, on paper, one way to win this fight and that is to knock Donald Cerrone out.
"Conor doesn't even do very well when a fight goes to a decision - and now, to knock a guy out who has an extra 15lb is the biggest talking point of the fight.
"It definitely helps Cerrone; I wouldn't call it a mistake but here is the mistake - not only is at 170lb but its a main event, You have a guy coming into a five-round fight who has openly admitted twice [that he gets fatigued].
"Now he's coming in after all this time off and he's walking into a main event for five rounds with a guy who likes to do what Conor does.
"Donald Cerrone has more ways to win this fight and people don't appreciate that if her can survive the first two-and-a-half minutes, his chances of winning this fight go up.
"Conor now has two things against him; 170lb and five rounds - after a lay-off."
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