Ronaldo signed a new long-term contract with Real back in September which will keep him at the Bernabeu until 2017.
"I wonder if ever the day would come when maybe he would come and play for us [Manchester United] again," Charlton told Laureus.
"I don't think it will happen, but you never know.
"He is the most enjoyable player to watch that I've ever seen. He is so fast, so inventive, just magic."
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