Ronaldo a doubt for Dortmund return

Cristiano Ronaldo is a doubt for Real Madrid's UEFA Champions League semi-final second-leg against Borussia Dortmund due to a thigh problem.

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 be a significant blow to 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 team-mates 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.