Ronaldo was speaking ahead of Sunday's UEFA Champions League final between PSG and Bayern Munich when he shared his view that Mbappe would be a better signing for his former club than Neymar.
"Right now, it is not that one is better than another, but if Real Madrid had to make a big investment, they should do so thinking about the future," the Brazil legend said during a webinar hosted by Santander.
"Neymar is 28 years old and Mbappe is 22. As an investment, it would be more logical to bring the younger [player]."
Both players were in action during Sunday's showpiece final but were unable to prevent the Parisians from suffering a 1-0 defeat at the hands of Bayern, who have now won the competition on six occasions.
Neymar scored 19 goals in 27 appearances for the season, while Mbappe netted 30 in 37 games, including 18 goals in the league which earned him in the Ligue 1 Golden Boot award.
