Despite sitting 16 points behind league leaders Barcelona in third, Los Blancos secured a 3-1 win at the Camp Nou on Tuesday to progress to the final of the Copa del Rey after a 4-2 aggregate victory.
The Portugal international admits that their form in the league has forced them to concentrate on the cup as well as the Champions League.
"Beating Barca is always a source of great motivation," Ronaldo told AS.
"La Liga is less important because we are a lot of points behind, we need to look more at the cup and the Champions League, but certainly we will go there to do our best."
Madrid host Barcelona in La Liga on Saturday.