The 35-year-old scored 450 goals in 438 matches for the Spanish giants between 2009 and 2018.
Ronaldo left Zinedine Zidane’s side to join Juventus for £99million in July 2018.
Marca claim the Portuguese star is already contemplating a move back to Madrid.
He has allegedly reached out to his former club in a bid to make his interest known.
The five-time Ballon d’Or winner will have to rebuild his relationships at the club.