Ronaldo returns to United next year after their Champions League pairing yesterday.
Ferguson said: "Great players, particularly forwards - Denis Law, George Best, Pele, Eusebio - they always take the ball no matter the challenges.
"There are different forms of courage and that one is the best one.
"You've got lads who will run through a brick wall but the courage to take the ball all the time is a fantastic courage.
"He always had that."