Ruiz Jr claimed "I wasn't that hurt" after climbing off the canvas to inflict a damaging defeat by flooring Joshua four times - their rematch for the world heavyweight championship is on Saturday, live on Sky Sports Box Office, with ring-walks at 8.30pm.
"He was definitely hurt," Joshua exclusively told Sky Sports. "You don't go down unless you are hurt. It's such a difficult thing to say when you're fighting, because the adrenaline is high. A car probably could have gone into both of us, and we would have found a way to get up. I got put down four times, and got up.
"The only reason I didn't walk out into the middle of the ring was because my gum-shield wasn't in. I was waiting for the referee.
"He said: 'Are you ready to fight?'
"I said: 'Yes'.
"I was waiting for him to put my gum-shield in my mouth. But he waved off the fight.
"Was I hurt? Not to the point where I couldn't get up and stand on my feet.
"Was he hurt? Not to the point where he couldn't get up. But he was hurt enough that he felt that punch, for sure."
The first fight in New York was stopped with Joshua on his feet, his gum-shield back in his mouth. Ruiz Jr has previously questioned whether Joshua could have continued.
Joshua explained: "I've got to learn from that situation, to be more responsible. Don't leave it for the referee to take responsibility. Take care of that situation.
"I don't think that I didn't want to fight on, because I wouldn't have got up. I would have stayed down. I was waiting for him to put my gum-shield back so I could continue to fight. Next time I will take more responsibility and say: 'I'm ready, ref, my gum-shield is in so let's go'.
"That's how I will deal with it, next time."
A tense build-up to this weekend's rematch has seen Ruiz Jr shed weight and Joshua add to his coaching team and crop of sparring partners.
Joshua initially attributed his shock loss to a "lucky punch", and Ruiz Jr bit back by labelling his best moment in the same way.
"He said my punch was from the gods, as well," Joshua said.
"[His] was a great punch. Boxing is about timing, millimetres. It was a brilliant punch, it was from the gods, you could not ask for a better punch.
"I believe it was a punch from the gods."
Asked if his own punch that floored Ruiz Jr was from the gods, Joshua replied: "It was, but what followed was not. It was a blessing that I put him down. It was from the gods that I was the first to put him down. I hope he has that in the back of his mind.
"When I say 'a punch from the gods', it's not that it was lucky. It was just the perfect punch that anyone could ask for, going into a world heavyweight title fight."
Construction on this purpose-built 15,000-seat arena began on October 7 and used almost 300 tons of steel to cover an area of 10,000 sqm at the center of historic UNESCO heritage site.
Watch Ruiz Jr vs Joshua 2 on Saturday, live on Sky Sports Box Office, from 5pm. Book it via your Sky remote or book it online here. Even if you aren't a Sky TV subscriber you can book and watch it here.