The Mexican-American shocked the world when he took the WBA, IBF and WBO heavyweight titles from Joshua on June 1 in New York.
Ruiz Jnr became the first Mexican to win a world heavyweight title when he stopped Joshua in the seventh round after dropping him four times in a dramatic clash at Madison Square Garden.
British star Joshua activated the rematch clause in the contract and Ruiz Jnr was convinced to travel to Riyadh for the rematch after initially expressing concern.
But, when he arrived in the Saudi capital yesterday for the first world heavyweight title fight in the country, he said: “It feels good (to be here).
“You know I made history in New York and I’ll make history again in Saudi.”
Joshua and Ruiz Jnr will face each other in a purpose-built 15,000-seater outdoor arena in Diriyah on the outskirts of Riyadh.
The venue is nearing completion this week and Joshua visited the site when he arrived in the Middle East on Saturday.
There has been plenty of debate about both fighters looking slimmer in their training camps than they did their first meeting.
“I saw videos where he looked slimmer. I don’t know if that’s an advantage or a disadvantage,” Ruiz Jnr said to Sky Sports.
“I don’t know if he will take the punches as well as he did when he weighed more.
“Me? People are saying I lost too much weight, I won’t be strong, he will move me around.
“I am losing eight pounds from what I weighed on June 1. I’ll still be the same, I’ll still be strong.
“AJ has always been in shape. He has always looked really good, really cut up.”
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