The 31-year-old has missed his side's last three games through injury having been forced off in the latter stages of the 3-0 win over Villarreal on April 20.
One of those matches was the first leg of the semi-final as Madrid drew a blank in a goalless draw at the Etihad Stadium last Tuesday.
However, he has now returned to training ahead of the return fixture at the Bernabeu and is expected to be fit to start when Manuel Pellegrini's side travel to the Spanish capital.
Ronaldo is the Champions League's all-time leading goalscorer and the top scorer in this season's competition too having netted 16 times in 10 games. He needs just one more goal to equal his own all-time single-season scoring record for the Champions League.