The 35-year-old enjoyed stints at both Camp Nou, and at Real Madrid, and although he admits that he remembers his time at the Bernabeu more fondly, he cannot help but admire the Argentine.
"I am more a fan of Real Madrid," he told Marca. "But there is no doubt that Messi is the best player in the world."
The Brazilian went on to praise Spain's footballing approach at Euro 2012, and commended his former coach Vicente del Bosque on his use of the 'false nine' during La Roja's tournament victory.
"Football has been changing. I think Spain did a great job without a No.9. I know Del Bosque very well. I had him as a coach at Real Madrid, and he always played me as a pure No.9.
"It depends on each game, the opponent and much more [as to what formation you play]. I think the No.9 will always exist and will continue to figure in the game."
Ronaldo represented Barcelona betweet 1996 and 1997, and after a five-year stint in Italy with Inter, returned to La Liga and made over 200 appearances for Los Blancos before leaving the club in 2007.