The duo have again been nominated for the Ballon d'Or - alongside Neymar - a prize they have shared the past seven years, with Messi winning four titles in a row and Ronaldo three.
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Debate over which player is more talented has raged on for some time, but Ronaldo, a three-time Ballon d'Or winner himself, said the Argentine was his pick of the pair.
"I choose Messi," he told Clarin. "I see Messi more complete. He does things in a most spectacular way."
The Argentina talisman has scored 12 goals and set up five in 17 matches in all competitions this term, while Ronaldo has netted 23 in 22 games, picking up seven assists.