Ronaldo, 33, has won the UEFA Champions League a record five times over the course of his career with Manchester United and Real Madrid.
After winning three successive European crowns with Los Blancos he made the surprise switch to Serie A for a club and league record €100m (R1.6b).
And Rooney, who spent six seasons with the five-time Ballon d'Or winner at Old Trafford has backed him to maintain his incredible success in Europe's elit club competition.
"He'll do what he's been doing for the last 10 years, he'll bring goals to Juventus and I fancy Juventus to win the Champions League this year solely for the fact Cristiano has gone there," Rooney told CNN Sport.
"As a person he's a nice guy, a family guy, works hard and he's always got his family around him which is great to see.
"He works hard and deserves all the credit he gets because he's put that effort in to be at the top."