Mbappe, 18, was strongly linked with a move to Madrid after helping fire Monaco to the Ligue 1 title last season.
Paris Saint-Germain eventually signed the teenager on loan with the view to a permanent deal, but Argentina legend Maradona has suggested that Los Blancos were in pole position at one point.
According to the 57-year-old, Madrid president Florentino Perez decided against signing the France international because of Ronaldo.
"For me, Mbappe is the revelation of football. I think he can surpass many," Maradona told AS.
"Why did they not sign him? I told Florentino to sign Mbappe. I told him when we saw each other at Fifa. He told me... 'but you know I have Cristiano'."
Mbappe has scored 10 times and registered seven assists in 21 appearances for PSG during the 2017-18 campaign.