"Alex Ferguson's record at United is unbelievable," He told Radio 5 Live
"If he was to win the title, he would have to be acclaimed as the greatest manager of all time."
Charlton added: "If it happens, then to do what he has done and to come back like that, when so many had written him off, would be fantastic.
"He keeps everyone happy and everyone at the club gives him their best. I'm very, very glad we have Alex."