There is no way Ronaldo will consider returning to Manchester United after his previous experience that led to him moving to Saudi Arabia. I also think he will rather accept a move to Sporting than return to United, and with the way things are playing out I think he might even retire at Al Nassr.
What if returns as a coach or sporting director, what will you say?
By the way, he loved Manchester United so much that he risked his reputation with the club by going on air and criticizing on how Manchester United is being mismanaged and why things have to change. So who knows? You could see Cristiano Ronaldo in the Manchester United dugout one day.
