Ronaldo available for Dortmund return leg
The Portugal international, top scorer in the latest edition of Europe's elite club competition with 12 goals, returned to training with his team-mates on Monday after sitting out Saturday's 2-1 La Liga victory.
He had damaged a thigh muscle in last week's 4-1 defeat in Dortmund.
The 10 outfield players who started against Atletico formed one group working on recuperation at training on Monday, Real said in a statement on their website.
"In the second the rest of the outfield players... worked with more intensity, including Cristiano Ronaldo," they added.
Even with a fit Ronaldo, Real face a stiff task against the Bundesliga side if they are to keep alive their bid for the 10th European crown that has eluded them since 2002.
"Cristiano is fine to play tomorrow," Mourinho said at a news conference previewing Tuesday's game.
The Portuguese added that he has a full squad to choose from, apart from injured full-backs Alvaro Arbeloa and Marcelo.