Leganes overturned a 1-0 first-leg loss to progress to the semi-finals of the Copa with a 2-1 win at the Santiago Bernabeu on Wednesday, although Ronaldo was left out of the squad.
And with Madrid 19 points behind rivals Barcelona in La Liga, retaining the Champions League again is Madrid's only realistic hope of adding silverware to the Supercopa de Espana they won at the start of the campaign.
Dani Carvajal admitted the Champions League is all that remains for Madrid to focus on and Ronaldo hinted at a similar target in a social media post.
"Cheer up team. Cheer up madridistas," Ronaldo wrote on Twitter. "We still have many battles to win."
Ánimo equipo. Ánimo madridistas. Aún nos quedan muchas batallas por ganar. pic.twitter.com/xkbCAMYmpk— Cristiano Ronaldo (@Cristiano) January 25, 2018
Ronaldo's future remains the subject of intense transfer speculation, although Manchester United manager Jose Mourinho has moved to play down rumours linking the Portuguese superstar with a return to Old Trafford.
"I think with the moment Real Madrid is having now, I think I should be the last one to add some fuel to the fire," Mourinho said on Thursday of a potential move for Ronaldo.
Madrid travel to Valencia in LaLiga on Saturday, with Zidane's side sitting fourth in the table, five points behind Los Che.