"Joseph Parker is a professional fighter...I got a lot of flak in New Zealand previously but I still feel that Joseph Parker is not a legitimate world champion," Hauser said.
Listen: Boxing historian Thomas Hauser on the Radio Sport Breakfast
"My sense is that Wilder would probably knock him out. I haven't seen any evidence that Joseph can punch hard enough to really hurt Deontay Wilder, or has the chin to take Deontay's punch. That said, Deontay is a flawed fighter.
"Would I turn on the TV to watch it. Yes, but would the winner be the heavyweight champion of the world? No. Right now Anthony Joshua deserves recognition as the number one heavyweight in the world. The winner of Deontay Wilder and Joseph Parker would be a credible challenger to that throne."
Hauser also challenged the view that heavyweight boxing was in a new golden era, saying it was still too fragmented. Whereas the famous fighters of the era when Muhammad Ali was in his prime had proved themselves, the current heavyweights had not.
"The way things are in boxing, you have to throw the belts out. There are so many champions out there," he said.
"Part of it is due to their skill, but more so because of clever manoeuvring and how the sanctioning bodies work. After Saturday night, Anthony Joshua is number one in the world. I'd like to see him challenged again and again and see what happens when it is all over.
"Joseph Parker has a belt and I'd like to see him develop his skills to a point he is a worthy contender. But going life and death with Andy Ruiz doesn't make you a world champion in any sense of the word in my book."
Meanwhile, Hauser hopes the ageing Klitschko retires but if he does continue, believes chasing a revenge win over Tyson Fury makes more sense than a re-match with the ever-improving Joshua.
"There is a lot of hype going on now but we really don't know how good these players are," he said.
"Anthony Joshua has the potential to be a great heavyweight champion, and also in terms of charisma and fan appeal.
"If boxing was a well run sport you would see the best fighting the best right away but that's not what is going to happen. There is some real momentum here...we'll see if boxing can build on this or shoots itself in the foot again."