Anthony Joshua believes Oleksandr Usyk is second only to Wladimir Klitschko on his list of toughest career opponents.
Joshua will take on mandatory challenger Usyk at Tottenham Hotspur Stadium next weekend after his planned fight with Tyson Fury was scrapped.
And he believes he has only faced a tougher test once in his career - legendary champion Klitschko at Wembley Stadium in 2017.
Joshua has lost before, to Andy Ruiz in 2019, but handily defeated him in their rematch later that year, and he ranks Usyk higher on that list of opponents than the American.
Speaking on BBC Radio 5 Live, Joshua said of Usyk: “On paper he sits No.2, behind Wladimir Klitschko.
"They're very different technically, but on paper he's an Olympic gold medalist, he reigned for over 10 years, he's No.1.
"But Usyk is No.2 because of his success at cruiserweight and then his success so far at heavyweight."
One of the big critiques of Usyk, who won gold at heavyweight at the same London 2012 Olympics Joshua won at super heavyweight, is his size.
He has struggled to impose himself against a lower calibre of opponent since making the move up after unifying the cruiserweight division.
He laboured to a lacklustre win over Derek Chisora last year, with some even saying that there's an argument to be made that he lost the fight.
And Chisora's power looked to cause him trouble at times, so stepping in with the much more refined Joshua could be a problem for Usyk.
And Joshua added: "One of his strengths is that he's getting in the ring with me. I've got to give him credit for that, it's going to be tough.
"He's a southpaw, he's been fighting orthodoxes his whole life, we fight southpaws once in a blue moon.
"I'm doing a lot of ring work, certain fighters do a lot of road works, pads, bags, shadow boxing.
"But with a southpaw it's all to do with positioning and we're doing ring work, a lot of southpaws are counterpunchers."
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Joshua believes the experience Usyk has against orthodox fighters will stand him in good stead.
But ultimately, the unified heavyweight champion thinks his work both in and out of the ring in training camp will see him earn victory.
"His strength is that he's seen fighters with my stance a million times, and knows how to position himself to land certain shots needed to be effective," he said.
"In this training camp I have had to adapt and learn to get around this new stance, because in the amateurs it was just backhand, left hook.
"My practice is much deeper than that, I've had to put a lot of power into my mind - I've done a lot of studying for this fight.
"He's a good southpaw fighter, he's seen guys like me a number of times and he's got a good chin so I need to look at the body."
