Former world champion Deontay Wilder views Oleksandr Usyk as a dangerous opponent for Anthony Joshua.
Joshua will stake his WBA, WBO, IBF, IBO heavyweight titles in a mandatory defense against Usyk, with their fight being targeted for September.
Wilder's upcoming opponent, WBC champion Tyson Fury, believes Usyk is "too small" for the division and expects Joshua to walk right through him.
Wilder disagrees with that position.
"Everyone is a threat until proven otherwise. Every fight is dangerous - you never know what night a person will have," Wilder said to Sky Sports.
Malik Scott, a retired heavyweight and head trainer of Wilder, agrees with his boxer's opinion that Usyk is a dangerous fight for Joshua.
"Usyk is a dangerous fight for anybody, not just Joshua. You have to commend Joshua for taking him on. Usyk is not a guy everybody is trying to fight - he is a guy that people would prefer not to fight," Scott said.
"Usyk is learning on the job against the most dangerous guys. He didn't go on a seven-fight plan. This is his third fight at heavyweight. That's a big climb. It will be interesting how Usyk responds to Joshua's size and technicalities, and how Joshua responds to Usyk's speed as a southpaw."
As a cruiserweight, Usyk unified the entire weight class when he dominated Murat Gassiev in the final round of the Word Boxing Super Series cruiserweight tournament in season one.
The Olympic gold medal winner has not looked as impressive in his short heavyweight run - with a much tougher than expected decision win over Derek Chisora in their twelve round encounter back in October of last year.