The British heavyweight faces Wach, a former world title challenger, ahead of Joshua's massive showdown with Ruiz Jr on December 7, live on Sky Sports Box Office.
Poland's Wach has proven his grit while extending Wladimir Klitschko and Alexander Povetkin into the later rounds and will be hoping to drag Whyte into a dramatic battle after rejuvenating his career with two victories in his home country.
Fellow Brit Tom Little will also be targeting a huge upset on the undercard as he takes on Mahammadrasul Majidov, the former world amateur champion.
Alexander Povetkin's explosive encounter with Michael Hunter has already been confirmed, along with Filip Hrgovic's step-up in class against Eric Molina on an action-packed evening of heavyweight fights.
The talented young duo of Hopey Price and Diego Pacheco will also be eager to impress at Diriyah Arena.
Matchroom Boxing boss Eddie Hearn said: "This wraps up a huge card for what will be a historic night for the sport.
"Ten big heavyweights will descend on Diriyah to cause a shockwave through world boxing as Saudi Arabia hosts one of the biggest heavyweight fight of all time. Ten days to go!"
Adam Smith, Head of Sky Sports Boxing, said: "Anthony Joshua's epic rematch night has even more heavyweight fireworks as Dillian Whyte battles Mariusz Wach on a bill which is brimming with big punchers.
"Whyte will be seeking to showcase his power against the battle-hardened Mariusz Wach, while the likeable Tom Little receives a dream fight against Mahammadrasul Majidov, the former world amateur champion.
"Hopey Price and Diego Pacheco are also keen to display their talent on a momentous night for the sport as we build towards Joshua's spectacular showdown with Ruiz Jr."
