Joshua, 31, suffered the second defeat of his career to the Ukrainian on September 25 in front of a sold-out crowd at the Tottenham Hotspur Stadium.
Usyk - who was the smaller man by a country mile - shocked the world by battering the Brit from pillar to post, a win which saw him become the third man, after David Haye and Evander Holyfield, to win world titles at cruiserweight then heavyweight.
Joshua's promoter Eddie Hearn has since confirmed he exercised the rematch clause in his contract with Usyk a few days after AJ's shock defeat, though a date for a second meeting between the pair has not yet been finalised.
Ruiz Jr knows a thing or two about rematches having lost the WBA, WBO, IBF and IBO unified heavyweight titles to Joshua in December 2019.
And the Mexican has warned the Ukrainian he cannot afford to let his concentration slip or else he will have to face the consequences. However, he admits he doesn't think that will be the case, as he feels his head is in the right place anyway.
"You know what, the sky's the limit, it's really all up to him to do the best he can," Ruiz Jr told The Last Stand Podcast.
“I wouldn’t want him to make the same mistakes I did.
“Getting all the belts, partying, doing all the dumb stuff, and not worrying about keeping those belts.
“I’m pretty sure Usyk is gonna [sic] do the right things.”
He added: "At first I thought Anthony Joshua was gonna [sic] manhandle him, I thought he was gonna be the bigger fighter, I thought he was gonna box him around just like he did to me.
"I thought he went in there without a game plan thinking he was just going to be the bigger and stronger guy but Usyk, he's a tricky fighter man, he's a lefty.
"All these heavyweights just throw one, two punches, they rely on two or three punches, and I feel that's where I come different and start throwing different bombs and combinations.
"But Usyk did an amazing job, he really surprised me, and you know he's a man of God as well, so hat's off to him."
Ruiz thinks it'll require some hard work from Joshua but has refused to write off his chances.
He said: "If he does a different game plan and maybe fights like when he fought me maybe he can get that victory.
"Because that fight was close, it was pretty close, until Usyk started dominating in the later rounds.
"But if Usyk pressures him, and counter punches him, I think it'll be the same result, yeah."News Now - Sport News