Ronaldo's new arrival is his first child with girlfriend Georgina Rodriguez.
The Portugal captain reported that both baby and mother were "doing great" in a post on Instagram that showed Ronaldo and eldest son Cristiano Jr posing alongside Rodriguez.
Ronaldo's household is set to be hectic with baby twins Eva Maria and Mateo, born of a surrogate mother, also in their infancy.
Though he has only scored once in LaLiga for Madrid, who trail Barcelona by eight points, Ronaldo has spoken of fatherhood offering him a fresh perspective, recently claiming it had "softened" him.
Photo Getty Images. Caption: Real Madrid superstar Cristiano Ronaldo and girlfriend Georgina Rodriguez