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Featured Image Credit: DAZN/PA
Ruiz, 31, sent shockwaves throughout the boxing world after he caused a stunning upset against Anthony Joshua in their world title fight at Madison Square Garden in June 2019.
Ruiz, who hasn't fought since his defeat to Joshua, has been training and working hard to regain his physique as he eyes up a 2021 return to the squared circle.
Ronaldo spoke with boxing star Gennady Golovkin about Ruiz's physical condition in the DAZN docuseries Parallel Worlds.
The 35-year-old Portuguese forward said that while two-time unified champ 'AJ' is "one of the best," Ronaldo insisted that "Ruiz is good."
'Triple G' agreed with Ronaldo when the five-time Ballon d'Or winner explained that preparation is much more important than body.
"That's what I was talking about with my friends, because they made fun of him and told me to look at Ruiz's fat body," Ronaldo said.
"I would tell them, 'Listen, the body doesn't matter. What matters is preparation.'"
Ruiz, who has teamed up with Canelo Alvarez's trainer Eddy Reynoso, has claimed that he is "back [on the] right track" and is "working hard preparing for whoever is next."
The former unified champ said: "I'm working hard preparing for whoever is next. Thank God we are on the right track.
"It's hard. I've never done this in my entire life. I never lifted weights. I never had a physical trainer like them. It's time to run. It's time to get it back. It's time to work hard."