Former cruiserweight world champion Tony Bellew is backing Oleksandr Usyk to become a heavyweight champion.

Last year, the Olympic gold medal winner unified the entire cruiserweight division when he dominated Murat Gassiev in the final bout of the World Boxing Super Series cruiserweight tournament.

Usyk would then score a brutal knockout over Bellew in the fall of 2018, an outcome which led to Bellew's retirement.

This coming Saturday night in Chicago, Usyk will make his debut as a heavyweight against very late replacement Chazz Witherspoon.

According to Bellew, he views Deontay Wilder as the easiest for Usyk to beat - when compared to other possibilities like Tyson Fury and Anthony Joshua.

While Wilder is tall, he doesn't have the mass of Fury or Joshua.

"Wilder [is the easiest to beat among the three choices], and that's an easy answer. Don't get me wrong, if Wilder lands on him then it's not going to end well for Usyk, but you can say that about any heavyweight who Wilder lands on," Bellew told Sky Sports.

"I just think [Joshua and Fury] are too big for him. Fundamentally, he's a much better boxer than all of them, and I include Fury in that, but he's just too small to compete with them for 12 rounds. I think the size of Fury and Joshua would be a massive advantage and I don't think Usyk could overcome it.

"For [Usyk's] weaknesses, I still think he's a little bit open and can be caught. Watching his amateur fights, there was always a reaction from him when he got caught clean, but no one has exploited that so far in the pros. His chin is up in the air sometimes and if that continues then it might get caught one time."