Ruiz, who was born in America but fights for Mexico, shocked the division in New York in June when he inflicted a first defeat on Joshua to win the WBA, IBF and WBO world titles.
Former Olympic champion Joshua was knocked down four times before he was stopped in the seventh round on his US debut, marking one of the biggest upsets in heavyweight history.
“I’m really hungry,” Ruiz said at a press conference to promote the bout on December 7 in Diriyah.
“A lot of people are saying I’m not training, that I’m not taking it serious but I’ve got all these belts, there’s a lot of responsibility to this. I’m going to try my best, keep these belts, have them back in Mexico.
“December 7 I’m going to make another history and I’m going to win here in the same fashion, the same way that I won June 1 and I’m going to prove everyone wrong.
“The hunger still remains, I don’t want 15 minutes of fame, I want it to last. I want to be a champion for more years.
“He’s more hungry, he wants his belts back so that’s what’s giving me more motivation. I only had a month, a month and a half to train for the first fight. This time we have a whole camp, so that benefits me as well.”
Joshua did not offer any similar predictions as to the outcome of the fight, adding: “I was up against a good challenger at the time and as I mentioned I was only champion until June the first.
“And as Andy’s champion right now, that will last till December the seventh until he has to put his titles in the air, two warriors go to war and the best man will walk out victorious. I’m really looking forward to the challenge.”