Derek Chisora believes former unified heavyweight champion Wladimir Klitschko, 44-years-old, could still be a force in the weight class.

Klitschko decided to retire in 2017, a few months following his stoppage loss at the hands of Anthony Joshua. Klitschko had initially exercised an immediate rematch clause, but then backed away from that scenario and decided to call it a day.

"Wladimir is a good fighter, the guy's in shape," Chisora told Sky Sports. "The problem is with him, it's straightforward, I don't know why he retired. He could still be causing commotion in the heavyweight game. What reason he retired, I don't understand why. He only lost to Tyson Fury and AJ, but if he wanted to come back, I think he can come back and knock some people out in the game."

Chisora was scheduled to return this month, against former unified cruiserweight champion Oleksandr Usyk. Their fight was postponed due to the coronavirus pandemic. A new date and location for their bout is being worked out.

Usyk made his jump to the heavyweight division last October.

As previously reported, Klitschko has offered to help Usyk prepare for the bout with Chisora.

Chisora is not worried about the possibility that Klitschko lends his sparring services to Usyk.

"For him helping Usyk, I'm happy with that, I'm cool with that. But he's not going to help him when he's inside the ring is he? With me. He can come help me too, if I ask for it too," Chisora said.

Chisora and Klitschko were scheduled to fight each other in 2010. Their bout was canceled after Klitschko withdrew with an injury. Two years later, Chisora lost a twelve round decision to older brother Vitali.