The King Abdullah Sports City Arena in Jeddah will also be the setting for Liverpool's Callum Smith's WBC title eliminator against France's reigning European Champion Mathieu Bauderlique.
The undercard also includes unbeaten Somali-British prospect Ramla Ali matching up against Crystal Garcia Nova in an eight-round Super-Bantamweight contest, which will be the first official women's fight in Saudi Arabia.
Former two-weight World Champion Badou Jack against Richard Rivera in a ten round cruiserweight contest. Andrew Tabiti and Tyrone Spong in an eight round heavyweight fight. Ukrainian light-heavyweight Daniel Lapin against Slovakia's Jozef Jurko and super-lightweight fight between Ziyad Almaayouf and Mexico's Jose Alatorre.
The Croatian Hrgovic (14-0, 12 KOs), who is ranked number 3 in the IBF rankings will slug it out with China's undefeated Zhilei Zhang (24-0-1, 19 KOs) in a final eliminator for the IBF Heavyweight World Title to decide who is named the mandatory challenger for the title held by Usyk.
"I respect a fighter like Zhilei Zhang, especially as there were plenty of others who could have fought me and didn't," said Hrgovic. "The respect stays outside the ring, and it'll be business as usual for me when I step in there and look to do what I do best; put people away.
"There's a huge amount at stake in this fight. I'm a fighter who belongs at the top of this division, and there'll be no doubt about this when Zhang is dealt with and I go on to beat whoever it is out of Usyk or Joshua. I'm entering my prime, and now is the perfect time to be putting myself up against the top fighters in this division. I will become the heavyweight champion of the world."
"I'm looking forward to August 20," said Zhang. "My team and I have been grinding every hour of every day for this fight. Hrgovic is going to be the toughest opponent in my professional career. A victory will secure me the IBF mandatory challenger position, which is why this fight is so important to me. I will be in the best shape I've ever been in."
Meanwhile, Smith was crowned the WBA super-middleweight World Champion in Septemeber 2018 in Jeddah and is looking forward to making a return as he a bid to set up a light-heavyweight world title fight against Artur Beterbiev.
"The last time I was in Jeddah I was crowned the best Super-Middleweight in the world, so I have fond memories of the place," said Smith.
"The whole experience was great, and the fans really got behind me, so I'm really looking forward to returning next month. I won't come away this time as a World Champion, but this is a tough fight on a great card and one which should set up a challenge at the number 1 in the light-heavyweight division."