The Madrid star is one of the best players in the world and won the FIFA Ballon d’Or award in 2014.
Forest striker Oliveira, 24, is a big fan of former Manchester United attacker Ronaldo and has spoken highly of him.
"When I was first called up to the national squad, I was 19 years of age, so I looked up to him," the Portuguese told BBC Radio Nottingham (on October 1).
"He is a big player, but he also works every day to do better. He is a great example to follow."
Oliveira has scored one goal and created two chances in three Championship appearances for Forest so far this season.
The Portugal international striker has a pass accuracy of 80% and a shot accuracy of 44%, and has won four dribbles and two tackles.
Forest are 14th in the Championship table at the moment with 12 points from 10 matches, six points behind sixth-place Burnley.