The Real Madrid forward has been linked with a return to the Red Devils after declaring he was “unhappy” at Los Blancos earlier this season.
The 28-year-old scored the decisive goal in a 3-2 aggregate victory over United in the Champions League last 16 last week and opted not to celebrate the strike.
And Charlton, who is widely regarded as one of United’s greatest-ever players, is optimistic Ronaldo could return to the Red Devils.
“Any great player would be welcomed back but Cristiano went beyond being just a great player,” Charlton told the Sun at Laureus Sports Awards in Rio on Monday night.
“He scores phenomenal goals, loves the club and was just the right sort of player at Manchester United. I’m a fan of him like anyone else and on a personal level I would like to see him back. I can’t say anything more than that.”
Ronaldo scored 118 goals in 292 appearances for United before completing a world-record £80m transfer to Real Madrid in August 2009.