The Portuguese has again been overlooked for the Ballon D'Or in favour of Lionel Messi, who has now collected the award on four consecutive occasions.
However, the superstar, who won it in 2008 in recognition of his phenomenal 42-goal contribution to United's Champions League and Barclays Premier League double, remains Messi's closest challenger.
And for the first time since he brought Ronaldo to Old Trafford, Ferguson will have to find a way of stopping the 27-year-old next month given Real Madrid lie in wait in the Champions League.
"Maturity brings many things," said Ferguson.
"When I went to see them play against City, some of his decision-making in terms of passing was brilliant. One-touch passing, good crosses.
"In the six years we had him, you just saw his game grow all the time, and he was a fantastic player. Now you see the complete player.
"His decision-making, his maturity, his experience, plus all the great skills he has, they all make him the complete player."
Ferguson is trying not to think about the best way to combat Ronaldo, preferring instead to concentrate on the players in his own squad and exactly who will be fit for the first leg at the Bernabeu on February 13.
Ronaldo, meanwhile, last night bagged a hat-trick to secure Madrid progression in the Copa del Rey at the expense of Celta Vigo.
The free-scoring forward did what he does best as Jose Mourinho's men turned around a 1-2 deficit with a 4-0 second-leg win.