Anthony Joshua faces the biggest test of his boxing career on Saturday (Dec 7) as he attempts to reclaim his world heavyweight crown from Andy Ruiz in a controversial rematch in Saudi Arabia.

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.

A leaner, meaner Joshua told reporters this week he is "hungry, determined and focused" for a bout that is expected to get under way at around midnight local time.

The stakes could not be higher for Joshua, who will 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 re-establish 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.

He 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 1.98m Joshua has invested heavily in quality sparring partners, hiring boxers of similar stature to 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."

He is also believed to have shed considerable bodyweight for the fight.

In June, Joshua weighed in at 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.

"Before I was trying to bench press a house. I used my body to get where I needed but then I started realising 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, says 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 US$60 million (S$81.6 million) while promoters Matchroom Boxing were handed an eye-popping US$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 US$9 million.

Matchroom boss Eddie Hearn believes Saudi Arabia has the potential to rival Las Vegas as a venue for boxing's biggest fights.

"Every boxer and every manager want to fight here," Hearn told The Guardian newspaper.

"(Manny) Pacquiao and Canelo (Alvarez) are coming. The talk is (Floyd) Mayweather is too. They want a piece of the action.

"The plan is to make Saudi Arabia the home of mega boxing. All due respect to Las Vegas, but this place has the ability to bring any fight they want here."

Yet the decision to stage the fight in Saudi Arabia has left the event mired in controversy.

The Saudis faced intense diplomatic fallout over last year's murder of dissident journalist Jamal Khashoggi in the conservative kingdom's consulate in Istanbul.

Under de facto ruler Crown Prince Mohammed bin Salman, Saudi Arabia has also mounted a sweeping crackdown on dissent which has seen dozens of women activists, journalists and political dissidents jailed during the past two years.

Activists accuse Saudi rulers of using glitzy concerts and sporting extravaganzas as a tool to try and soften their international image, so-called "sportswashing".

Promoter Hearn has shrugged off the criticism however, insisting that "no-one has the right to tell a fighter how and where they can earn their money".