Anthony Joshua has been warned that Oleksandr Usyk is "a big, big, dangerous threat" to his WBA, IBF and IBO heavyweight belts.
Joshua faces former unified cruiserweight champion Usyk at the Tottenham Hotspur Stadium on September 25 and Tony Bellew believes the British champion has a difficult opponent to get past.
Bellew thinks AJ can get the job done against his older, but dangerous 6ft 3in opponent, but says it will not be a walk in the park.
Former world cruiserweight champion Bellew has lauded Ukrainian Usyk's footwork and described the unbeaten 34-year-old as "technically perfect".
Bellew lost to Usyk in November 2018 and then retired after the eighth-round stoppage in Manchester. And Bellew knows more than most that, despite fighting for the most of his career at cruiserweight, Usyk is a big threat in the heavyweight division.
Bellew told The DAZN Boxing Show: "Believe you me mate, he hits hard enough to send me down.
"He's exceptional. He's the best I ever faced. He is so technically perfect. His footwork is on another level.
"Sometimes (you) just gotta hold your hands up and say I lost to the better guy. He is better than me. He is fantastic, phenomenally gifted in everything that he does.
"My only worry, which I've become friends with them and I speak to him, was don't go too big. I just feel like it's going to be size that beats this man.
"No one is going to outbox this guy. "No one's going to be outboxing the man, leading the dance.
"Nobody in the whole world, not even Tyson Fury is going to lead this merry dance, purely because his feet are so good that Tyson will be a little bit lost.
"I think Tyson will try and bring him to them because if you chase and attack someone like Oleksandr, it's what AJ needs to do because it's the way AJ can do it, and AJ is a good enough athlete and quick enough with the feet to get there.
"Fury isn't. So Fury will use his size and try to overcrowd him, get close to lean on, make it messy, make it hard."
'AJ will be losing when he stops him'
Bellew, a friend of Joshua's, thinks the Watford-born fighter could be behind on the cards when he finally gets on top of Usyk to stop him.
Bellew added: "For someone like AJ, I believe AJ is going to be losing when he stops him. I think he'll be behind on points. I think he catches up with him about rounds eight or nine.
"Hopefully, it can be quicker. If he lets the gap get too big, then this boy can get away with it. Trust me, he's a threat. He's a big, big dangerous threat.
"People are overlooking the fact that he's a cruiserweight. Don't think about him as a cruiserweight. Just think about his actual technical ability and what he's capable of doing in a boxing ring. This guy can make people look ridiculous."