The Spain international also hails the Portuguese forward as "a complete player" and is impressed with his all-round game.
"He is the most ambitious player I have met, with his hunger and desire to score in every game," Alonso told UEFA.com.
"He is impressive in terms of his athletic qualities and his technical abilities. He is a complete player: he has a great shot; he knows how to put his opponent off balance in one-on-one situations; he's great at finding space; and he has great timing."
Ronaldo and Alonso both joined Madrid in 2009 from Manchester United and Liverpool respectively.