The Portuguese forward missed Madrid's 4-0 win at Real Sociedad on Saturday because of a persistent knee injury.
However, the 29-year-old appears poised to return to action in time for the midweek European test, after the club confirmed that he had undergone a "recovery session" prior to the quarter-final decider at Signal Iduna Park.
Real lead 3-0 from the first leg at the Bernabeu, Ronaldo finding the net in a comfortable victory for Carlo Ancelotti's men.
The former Manchester United man's presence will undoubtedly come as a boost as Real aim to finish off the tie and progress to the last four.
On his reasons for leaving Ronaldo out of the Sociedad clash, Ancelotti said on Saturday: "We had to avoid injury so I rested Cristiano."
Angel Di Maria is also in contention to feature in Germany, taking part in training after recovering from illness.
