Cristiano Ronaldo to Sporting Lisbon is great likely to happen than Cristiano Ronaldo to Manchester United. After what he recently faced with the club, he will not have such thoughts, not to even swing our way. Manchester United are currently building a squad who can lift the Premier League Competition in the next three to four seasons. The offers are tempting and I must say Ronaldo deserves these bumber deals.
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.
And in fact, Ronaldo did not leave both of them for now, he will stay in An-Nassr at least until June of 2027. There are still 2 years left for him to be at the club, especially since An-Nasr's coach is also from Portugal.
He is currently 40 years old, meaning that to end his career, that means he is at least 42 years old. Is it possible that he will still return to Sporting to end his career? I actually think more that he will stay at An-Nasr until the end of his career. But, I don't know where he will go in the next 2 years.