Alonso played with Ronaldo at Real Madrid before the Spaniard made the switch to the Bundesliga champions back in 2014.
The 35-year-old is still a big admirer of the Portugal captain and admitted Bayern could use someone of Ronaldo's quality.
"Cristiano has adapted on the pitch. He's not a central striker, [but] he wants to play closer to the area," Alonso told Onda Cero. "He intuitively knows where the ball will go - a lot of goals are scored with his first touch.
"I think he's done very well, having taken this step and getting closer to the area. As long as he's getting 50 goals, I wish we had someone like him here. Cristiano's numbers are amazing, indisputable."