I don't think yet with team like Real Madrid and Juventus want to sign in again due Ronaldo age have been 37 years old and actually he doesn't at the top performance right now trough when he still under 30 years old. Realistic for Ronaldo joined wit MLS league before retired from football or he could try playing at small team but doubt want to pay expensive salary from Ronaldo. Probably Ronaldo have bigger ambition keep trying to play on higher level club exactly have team participants on Champion League.
Real Madrid and Juventus let Ronaldo leaving their clubs even back in those years, Ronaldo still performed very impressively. Now his performance is decreasing to the bottom of his career so it would be no reason for these clubs to sign with Ronaldo. The drama and reaction of Ronaldo in Manchester United make other clubs have to consider more. It would be terrible to have a player who can bring conflicts to a coach and other players.
Can't stoppable with Ronaldo ambition actually he want play at European team and ever rejected most fantastic offer from Asian team because he want end his career keep playing at Champion League.
Ronaldo is very ambitious but he must accept a fact that no player can maintain their performance at top of the world forever. Look at Ibrahimovic, he returned to AC Milan and had one and a half of season very impressive. But in the past two seasons, his body is no longer well and his performance is decreasing a lot. However Ibra still felt happy and agreed with his position. Ronaldo should change himself and learn from Ibrahimovic if he wants to continue his career.