Before the start of the 2018-19 campaign, Ronaldo ended his nine-year stint with Los Blancos in order to pen a long-term deal with Juventus.
However, after reports began to emerge linking the Portugal superstar with another spell at the Bernabeu, compatriot Fonte feels that a reunion with the La Liga giants is a possibility.
Speaking to talkSPORT, the Lille defender said: "I know he loves Madrid, that's for sure. It's clear that he loves the club itself, it's one of the biggest clubs in the world, if not the biggest.
"He's left many, many friends there and he's always left the door open. So I wouldn't be surprised if he goes back to Real Madrid."
Ronaldo still has over two years remaining on his contract at Juventus.