Even at home, where he has sold out Wembley and Cardiff arenas, Joshua's demand would significantly dim.
That's the ruthless nature of this brutal industry.
Eddie Hearn and Joshua undoubtedly underestimated Ruiz last time around when they whisked him up on short notice to replace American Jarrell Miller, who failed multiple drugs tests, last June.
Ruiz, the once maligned Mexican heavyweight, was only ever supposed to be another notch on Joshua's record.
Instead his hand speed, pressure, angles and left-hook embarrassed Joshua at Madison Square Garden on his American debut, dropping the champion four times to capture the WBA, WBO, IBF titles with a seventh-round stoppage that stunned the sporting world.
On the way to fashioning his previously unblemished record Joshua never appeared the perfect pugilist.
Dillian Whyte and Klitschko rocked him. Joseph Parker went the distance, admittedly in the Cardiff spectacle that never got going. Carlos Takam held his own for 10 rounds, too.
No doubt Joshua boasts lethal power but his chiseled frame has endured frequent criticism for its robotic movement.
Defensive vulnerabilities have long been probed – Parker securing his title shot after a sustained campaign in which he and manager David Higgins claimed Joshua had a "glass jaw" – but never truly exposed until the unsuspecting Ruiz floored heavyweight boxing's glamour figure.
Six months on from that fateful night and the landscape Joshua and Ruiz enter the ring could not be more contrasting.
Since achieving his life-long ambition, Ruiz's world has changed irrevocably. He's appeared on talk shows, met the Mexican president, bought a lavish new home and high-end cars.
He no longer has the element of surprise but, this time, he's had a full camp to prepare.
The technical nous he's gained during an extensive amateur career combined with his fearlessness to walk forward, close the distance and unload with fast combinations perplexed Joshua in their first fight.
What's to say Ruiz can't do it again?
The challenge now he probably needs another knockout or, at the very least, a clear and decisive victory.
Judges in these high-profile instances near always favour the money fighter. And in this case, despite losing his aura, Joshua remains the drawcard.
At least this time no one is mocking Ruiz's misleading appearance.
Predictions of a knockout seem to forget Ruiz has never been stopped – his only professional defeat coming via a knife-edge decision to Parker in Auckland for the vacant WBO title three years ago.
Had that fight been staged in America or Mexico, it could well have been ruled a draw.
Differentiating fact from boxing fiction is never easy. Depending on whom you believe, Joshua has knocked out several sparring partners or been hurt himself in the build up to this fight – the latter possibly planted as a convenient excuse for defeat.
One aspect we know for sure is Joshua won't again overlook Ruiz.
From fellow Brit Lennox Lewis against Hasim Rahman to Mike Tyson reclaiming his WBC and WBA titles after his shock loss to James "Buster" Douglas, dethroned champions often respond.
For all the nerves and pressure Joshua may feel the fire should be back burning within. He appears to have embraced the challenger mindset. Adapting his training for more boxing specific work over strength and conditioning has also revealed a much leaner frame.
Clearly, this is no straightforward revival but Joshua doesn't need the statement stoppage many are demanding.
Be patient. Revert to basics. Regaining the belts on points by using his natural height and reach advantages should be Joshua's focus.
The other intriguing element of this card is the surprise return of Whyte.
Back in July, days after Whyte's unanimous decision victory over Oscar Rivas, news broke that the Englishman had failed a drugs test - yet he was somehow still cleared to fight.
Five months later and the legal disputes continue with United Kingdom Anti-Doping yet to release their findings.
Whyte is, therefore, allowed to continue fighting under this controversial cloud, despite serving a previous two-year doping ban in 2012.
After a period of laying low which coincided with his slide down the rankings, Whyte makes his return against fading Pole Mariusz Wach.
He could then be banned in the coming months.
Just another day in the murky boxing world, one where Joshua's credentials, his heart and hunger, will be revealed this weekend.
