Ronaldo was shocked by the jeers from home fans aimed at him during the defeat to Barcelona on Saturday night.
The Portuguese spent the Sunday bunkered down at home with his family, stunned by the backlash.
And Sport says Ronaldo is now seriously considering quitting Real at the end of the season to return to England.
Manchester City owner Sheikh Mansour, confirmed by Ronaldo, made the attacker an amazing offer last year, which he turned down. Former club Manchester United would also be in the hunt, where manager Sir Alex Ferguson has spoken regularly about re-signing his former protege.