The Argentina striker says his compatriot is unrivaled in the modern game and backed him to be crowned the best player in the world again.
Messi - who has been crowned the world's best player a record four times - goes up against the Real Madrid star and Bayern Munich's Franck Ribery in the battle for the award Monday.
Ronaldo is the favorite to land the prize, with injury hampering Messi's last 12 months, but that hasn't stopped Aguero from backing his international teammate to add a fifth Ballon d'Or to his mantelpiece.
He told ESPN: "Messi — he comes from another dimension. To me, he'll win the Ballon d´Or. Cristiano [Ronaldo] played well in Madrid but Messi will always be better even if he only scores a goal a year."
Despite his injuries, Messi still ended 2013 with 45 goals in 46 games in all competitions.