Brazilian Messias joined Milan last week from Crotone, having broken into Italian football at Serie D level.
Ronaldo told La Gazzetta dello Sport: “It's important that they are back in the Champions League, at this level.
“Milan are competitive again in Serie A and in Europe."
On if he was aware Messias, he added: “Honestly, no. I follow Serie A, but I haven't seen much in the new season, I concentrated on the players to be recruited for Valladolid."
Ronaldo also backed Zlatan Ibrahimovic for a big season.
"Ibra is very strong, the years don't count for him," Ronaldo continued. “He's a rock, he has a body of a 30-year-old, not 40.
“He will guarantee the usual results because he knows how to manage himself like a super professional.
“He came to visit me in my holiday home in Ibiza. A fantastic day, we had fun, we talked a lot, about football and more. He arrived with his family, with his very good children."
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