Six months after suffering a shock knockout defeat to Ruiz at Madison Square Garden, Joshua will climb back into the ring with Ruiz seeking to win back the IBF, WBA, and WBO titles, AFP reported.
A leaner, meaner Joshua told reporters this week he is "hungry, determined and focused" for a bout that is expected to get underway at around midnight local time.
The stakes could not be higher for Joshua, who would face a long road back to the pinnacle of the heavyweight division if he loses a fight being hyped as "Clash on the Dunes."
Victory, by contrast, would reestablish his credentials in the division, opening the door to money-spinning fights against WBC champion Deontay Wilder or fellow Briton Tyson Fury.
"I am not here to put on a show, I am here to win," Joshua (22-1, 21 knockouts) said.
Joshua has blamed a "lack of experience" for his defeat to Ruiz in June, when he was knocked down four times en route to a seventh-round stoppage.
For the rematch, the 6ft 6in (1.98m) Joshua has invested heavily in quality sparring partners, hiring boxers of similar stature to the 6ft Ruiz to prepare for the fast-handed Mexican-American.
"We had to bring in hard, rough sparring partners," Joshua said. "I brought in the toughest and roughest."
'Punching like a horse'
Joshua is also believed to have shed considerable bodyweight for the fight.
In June, Joshua weighed in at 247.8 pounds (112.4 kg) but has said this week he expects to tip the scales significantly lighter, having cut muscle bulk in order to improve his mobility around the ring.
"I may be less than 17 stone (238 pounds)," Joshua said of his expected weight.
"Before I was trying to bench press a house. I used my body to get where I needed but then I started realizing the sweet science of the sport," he said.
"I am punching like a horse kicking backwards right now."
Ruiz, whose slick, swarming combinations rocked Joshua in their first meeting, said he is ready for the Briton's likely change of tactics.
"I know (Joshua) is going to come with a different game plan, I know he's prepared and I know he's motivated," said Ruiz (33-1, 22 knockouts).
"I know he's lost weight and will try to box me around, but it's just my job to prevent that. I'm ready for whatever comes my way."
Win or lose, Saturday's eagerly-anticipated heavyweight battle could signal the dawn of a new era for boxing.
The rematch will be taking place in a purpose built 15,000-seat arena in Diriyah on the outskirts of the Saudi capital Riyadh.
Saudi Arabia secured the staging rights to the rematch after reportedly offering an astronomical purse to promoters and fighters.
Joshua's take is reported to be around $60 million while promoters Matchroom Boxing were handed an eye-popping $40 million site fee to award the fight to Saudi Arabia.
Ruiz, who was locked into a rematch at a set figure as a condition of his first meeting with Joshua, is expected to receive $9 million.