Bellew claimed a world title last time out on his third attempt when he beat Ilunga Makabu in three rounds at Goodison Park.
The Merseyside man is unbeaten in seven bouts since stepping up a division from light-heavyweight but looks set for his biggest test against Flores.
Haye believes his fellow Brit has underestimated the American and expects that Flores will claim the world title at his first attempt.
“I don’t think Tony is going to win the fight. B.J. is a big cruiserweight. Look at them next to each other, there’s not a lot in it at first sight, but Tony is tall and skinny whereas B.J. is wide and thick set and can punch,” Haye said.
“B.J. is very underrated, he hasn’t perhaps performed to the best of his ability in his big fights, but he’s been boxing since his was six, has great amateur pedigree boxing all over the world, and I think Tony has underestimated him.”