Terence Crawford has been warned about the significant disadvantage in size and weight that he is about to confront.

On Saturday at the Allegiant Stadium in Las Vegas he moves up to super middleweight from junior middleweight to challenge the undisputed 168lbs champion and does so having won his first title at 135lbs.

In the 35-year-old Alvarez he is also encountering an opponent who has previously won a title at light heavyweight, and one he was ultimately not expected to fight.

The retired Kell Brook was stopped by Crawford in 2020, four years after Brook lost for the first time when being stopped at middleweight by Gennady Golovkin – Alvarez’s greatest rival and the opponent he shared the ring with for 36 rounds.

Brook, a career welterweight, was overpowered that night in 2016 by Golovkin, and having never fought beyond middleweight is wary on Crawford’s behalf of the size and strength Mexico’s Alvarez will have.

Crawford moved up to 154lbs to defeat Israil Madrimov in 2024 and both for that fight and since then has enhanced the physique that delivered to him the undisputed titles at 140 and 147lbs. The retired Brook, of England, expects the physicality of 168lbs to feel greater to Crawford than it may appear on the scales, and for it to prove influential regardless of his belief that Alvarez is in decline.

“I don’t think it’ll look like there’s a big difference, but when you’re in there – when I was up against Golovkin – just the presence of that kind of fighter, you completely know the difference,” Brook told BoxingScene. “I boxed all my career at welterweight, moved up to middleweight, and you can just feel it – obviously I felt it. Golovkin’s obviously a [future International Boxing] Hall of Famer – he’s gonna know pretty quickly that he’s in with a super middleweight, and he’s gonna feel that force.

“I don’t think he’s the fighter he was. But he’s still a great fighter. That’s what I mean – that’s why I’m so interested about this fight because he’s on the slide a little bit, and the weight. Who can perform at this level – the magnitude of fight? Even though I believe they both can, Canelo’s obviously been in with the better fighters. It’s very interesting, from the first round. How’s the fight gonna get sized up?”

Brook, who also fought and lost to the biggest of welterweights in Errol Spence in the years after dethroning Shawn Porter as IBF champion, was then asked if Crawford was the best he fought, and he responded: “Yeah. He’s got to be.

“His skill. He’s a very, very skilful fighter. I can’t see there being much difference in that. Terence Crawford’s a very good operator; he can switch hit; he’s very sharp. All the world’s gonna be watching. It’s exciting. Is size going to be a factor in this fight? That’s what I feel.

“He can be hurt – I know he can be hurt. Canelo’s a great finisher, and he can be hurt – we’ve seen him in previous fights he can be hurt. He won’t have got a better chin than Canelo. It’s hard to split them, really. It’s just the size, with Canelo.

“[My plan against Crawford was] to use my skill; to get to him and counter him and eventually get him, but it didn’t work out.

“[Alvarez is] very efficient. He doesn't waste shots. He’s got very good movement. He’s in it from a young kid – he’s a super fighter and he can adapt, and his record speaks for itself and what he’s done. He finds a way to win. 

“I’m leaning towards Canelo, but I still wouldn’t be surprised if Crawford did win. I still lean towards Canelo, and I see him beating him on points. It’s gonna be a magnificent fight.”