WBA, IBF and WBO champion Joshua was originally set to face Jarrell Miller in a heavyweight showdown in New York City on June 1, but that bout was scrapped after Miller failed drugs tests.
Ruiz stepped up to take Miller's place, with the American-born 29-year-old – who is of Mexican heritage – having won 32 of his 33 professional fights.
On Wednesday, Joshua urged current WBC champion Wilder to clear the path for an undisputed heavyweight title fight, should the Briton beat Ruiz.
Chances of that bout have now decreased, though, with Wilder having announced a rematch with Luis Ortiz.
And in a news conference ahead of his debut in the United States, Joshua insisted that he will have to take Ruiz just as seriously as he would Wilder or Fury.
"Without overlooking Andy or his team at all, as a fighter, you always look at the next fight," Joshua said.
"But fighting Andy for me is just as dangerous as fighting Wilder or Fury. They all possess their own skills, and it's a banana skin fight for me.
"I've got to take Andy deadly seriously, I won't overlook him at all. I respect him and his team, and that he put his name on the line to accept this challenge.
"No challenge is easy, as we all know he's going to give me a real fight, and it's down to me as a champions to box smart, clever and outmuscle Andy to get the win. Right now I'm only champion until June 1."
— Anthony Joshua (@anthonyfjoshua) May 29, 2019
Ruiz, meanwhile, believes that he is taking on Joshua – unbeaten in his 22 professional fights – at just the right moment.
"I've been waiting for this all my life, training so hard," Ruiz said. "I think this came at a perfect time, to fight against Anthony.
"I'm ready for June 1, ready to become the first Mexican heavyweight champion of the world. I'm ready to take those belts to Mexico.
"I don't have anything bad to say about Anthony. He's a champion, I'm a fan of him, I respect him. But inside of the ring there's going to be no respect, no fans, no friends. I'm going to give it all I've got."
Photo Getty. Caption: Anthony Joshua and Andy Ruiz Jr