Charlton is already there alongside Denis Law and the late George Best after an unveiling ceremony on Wednesday for the so-called Manchester United trinity.
The figures look out to another statue, built in the memory of former manager Sir Matt Busby.
Asked who might be next in line for a statue, Charlton, whose appearance record was beaten by Giggs, said: "Alex Ferguson and Ryan Giggs will be here. What more can they do? They deserve it."
Ferguson and Giggs have both won an astonishing 10 Premier League titles - United retained the crown by beating Wigan on the final day.
Charlton said: "Alex is just a sensational manager and I'd put nothing past him.
"He doesn't bother about hurdles. He goes straight to the problem, solves the problem and gets our team to play to their absolute maximum.
"You can't ask any more than that. We've all seen what he's been doing for 22 years."