The Portugal winger is favourite for the FIFA World Player of the Year award, mainly because of his scoring ability after claiming 37 goals already this season for his club.
And Ferguson is delighted with the player's attitude.
He said: "Success can affect people, no question of that. We see it time and time again.
"But I do not see any signs of that in Ronaldo. The boy is intelligent and sensible enough to realise what football is about.
"The great quality is to keep your ability - and your feet on the ground. Yes, he will go and express himself in a way that is extravagant at times.
"But that is a measure of his courage and real ability. We will never stop him doing that.
"We want players like him to perform on the stage at Old Trafford and express themselves."