Britain's unified champion makes his US debut against Ruiz Jr at Madison Square Garden on Saturday night, live on Sky Sports Box Office, and a punishing training camp appears to have taken its toll on Joshua, who has an inflamed right eyelid, a swelling under his left eye and a cut on his nose.
But the unbeaten 29-year-old dismissed the significance of his facial injuries, joking about how he sustained them during a sparring session.
"What happened right, I was sparring a lion, because I really want to take this camp seriously," Joshua told Sky Sports.
"It's just been tough, difficult training. I'm a fighter so the scars and stuff - look at my hands and stuff.
"That's just another added war wound to my list of scars so that's all it is."
Trainer Rob McCracken insisted he was pleased with Joshua's preparations, despite Ruiz Jr being introduced as a replacement after Jarrell Miller failed a drug test.
"It's been a good camp. He's in good shape," McCracken told Sky Sports. "The Miller change was difficult, but Ruiz is a better fighter I think.
"A similar style, comes forward, puts pressure on, but AJ adjusted. He's worked hard. Good sparring and good sparring partners as well. He's focused on the fight.
"Ruiz is a top-level fighter and he's dangerous."