It is now only two weeks until Joshua faces Usyk in an eagerly-anticipated rematch in Jeddah, Saudi Arabia on August 20.
Joshua foolishly attempted to outbox Usyk in their first fight last September at The Tottenham Hotspur Stadium.
Unsurprisingly, this did not work. The former undisputed cruiserweight champion outclassed the Brit and even hurt Joshua towards the end of the fight.
"He's under no illusions. He's going to have to be the best he's ever been to beat Usyk. I think he's going to have to be better than he's ever been. Better than the Wladimir Klitschko night. I feel like he has to be Klitschko-esque. That night there were ups and downs and he had to come back. He might just have to do that," Clarke told Sky Sports.
"He's got every chance. From what I've seen him put in on a daily and a weekly basis, he's given himself every chance and that's all you can ask from a fighter in a camp. If you give everything you've got to give, with the experience and the skill he's already got, he's given himself every chance.
"There's a lot of people out there talking about Usyk being so good and this and that. He is very good. There's no doubt. He's a great fighter. But he's a human. If AJ hits him on the chin more than once, he's only human, he goes down, he probably doesn't get back up.
"If Joshua gets a sustained combination on anyone in the world, boxer or not a boxer, possibly even animal or tree, he goes through them.
"I've sparred hundreds of rounds with him. I think of this thing of 'he's gun shy' - he wasn't gun shy when I've seen him in sparring, believe me.
"I feel like he's a nice guy. I think someone had to pull the bad guy out of him. I think Robert Garcia was good to do that. He pulled out the not give a [stuff] about anyone apart from winning this fight. He's brought it out of him.
"This could be Britain's greatest night of heavyweight boxing. I feel like everyone's putting him as a massive underdog and he might just get outboxed for 12 rounds. But you'd be daft to bet again him."
Joshua has seemingly looked to return to his roots ahead of the Usyk rematch.
He has had a change of trainer as he is no longer working with Robert McCracken. Robert Garcia and Angel Fernandez will instead be in his corner.
It is conceded that Joshua needs to be far more aggressive in the rematch and he has to use his power and strength advantage to weaken Usyk.
Even that may not be enough, as the two-weight world champion is a supreme talent and a genuine pound-for-pound great.
A win over Usyk would certainly top Joshua's victories over Wladimir Klitschko and Andy Ruiz Jr.
If he does reclaim his belts, the allusive Tyson Fury fight *hopefully* becomes more likely.