Alexander Krassyuk, promoter of former undisputed cruiserweight world champion Oleksandr Usyk, is very confident about his boxer's ability to compete with the biggest heavyweights in the sport.

On September 25, Usyk will have the biggest challenge of his career when he faces WBO, IBF, IBO, WBA world champion Anthony Joshua before a packed house at Tottenham Hotspur Stadium.

Usyk (18-0, 13 KOs), 34-years, was far from impressive in his two heavyweight bouts - including a tough decision win over Derek Chisora in October 2020.

Both Usyk and Joshua captured gold medals in the 2012 Olympics - with Joshua being the top man at super heavyweight and Usyk getting his medal at heavyweight.

Usyk is widely viewed as the having the edge in skill and speed, with Joshua (24-1, 22 KOs) being the naturally bigger man.

Krassyuk explains that Usyk has been working hard on his body to become a legit heavyweight - and brushes off comparisons to past fighters like Chris Byrd, who many felt was a natural cruiserweight competing at heavyweight.

"Boxers can just throw a punch to the chin and hope to get lucky, and they might be once out of 10, but can they do it 10 times in a row?" Krassyuk told ESPN.

"You have to box and win each and every round to win the title. Boxing is the art of defense first and foremost, landing punches and not getting anything back. Footwork is the basis for throwing punches and defending. This is very important for any fighter, and Oleksandr is very good at this."

"[Usyk] has been working hard ... building his body for the heavyweight division, and he's a true heavyweight now. No one can say he is a cruiserweight fighting as a heavyweight like Chris Byrd was. Oleksandr is a natural heavyweight now."