Within the next two weeks the fight will get confirmed and while there have been reports of the contest being pushed back to mid-August, Planet Sport has been told July 23 is still the date in mind.
Joshua is bidding to become a three-time heavyweight champion following his points defeat to Usyk last September.
And Hearn is backing AJ to reclaim the WBA, IBF and WBO belts.
The Matchroom Boxing chief said on an Instagram live: "I'm telling you now, AJ KOs Usyk within six rounds."
"I rate Usyk but I believe in Anthony Joshua and I believe he's going to put it right in the rematch, I really do."
Who will the winner fight next?
There are a number of options for Joshua and Usyk, including an undisputed clash against Tyson Fury.
The 'Gypsy King' has claimed to have retired from the sport but remains the current WBC titleholder and is expected to continue fighting.
Should Fury not return though, then the next big name is Deontay Wilder who confirmed he will continue boxing. He is desperate to become world champion again and would not dodge a fight with either Joshua or Usyk.
Other contenders include former world champions Joseph Parker and Andy Ruiz Jr while Dillian Whyte, Joe Joyce and Frank Sanchez are also high in the world rankings.