Ronaldo a doubt for Dortmund return
Ronaldo, who missed Real's 2-1 win at Atletico Madrid on Saturday, suffered the injury in Real's 4-1 defeat to the Germans in the first-leg last Wednesday and his absence would significantly hamper any hopes of a comeback.
"Cristiano Ronaldo exercised alone on the pitch alongside physical trainer Carlos Lalin," a statement on the club's website said on Sunday as the majority of his teammates took part in a recuperatory session.
Ronaldo is currently the Champions League's top-scorer with 12 goals and has scored in each of Real's last six European games.
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