Champions League: Will Ronaldo be fit for Dortmund clash?

Real Madrid top scorer Cristiano Ronaldo's participation against Borussia Dortmund in Tuesday's Champions League quarter-final second leg is still in doubt with the player nursing a knee problem, coach Carlo Ancelotti said on Monday.

Italian Ancelotti rested the Champions League top scorer for Saturday's 4-0 La Liga win at Real Sociedad but said he was ruled fit to play as the Spaniards arrived in Germany with a 3-0 advantage from the first leg last week.

"Cristiano always wants to play and I want him to play. But he is a professional and he knows when he cannot," Ancelotti told reporters.

"He is having treatment and yesterday he trained at a reduced intensity. If he is 100 percent he will play and if not he won't. We have never taken risks with him or any other player."

Ronaldo took part in the final training session in Dortmund but broke off before the end.

The Portugal captain, who has a record-equalling 14 goals this season in Europe's elite club competition, has complained of discomfort in his left knee.

Ronaldo made his 100th Champions League appearance in the first leg at the Bernabeu and his goal matched Lionel Messi's single-season record set in 2011/12.

Real ideally would need the Portuguese's attacking skills to counter Dortmund, who will go out looking for an early goal that could boost their chances of turning things around.

The Germans will have their top scorer Robert Lewandowski back in the team following a suspension in the first leg.

"With Lewandowski returning this is a different game," Ancelotti said.

"His presence lifts his fellow players.

"We will have to keep the balance between attacking and defending but we are best at attacking and we should show that."

Lewandowski had scored four goals against Real in the semi-final last season as Dortmund advanced to the final only to lose to Bayern Munich.

"Dortmund will want to go out and score a goal in the first 15 or 20 minutes," defender Daniel Carvajal told reporters.

"They will put a lot of pressure on us and we have to be ready for it. Why should we not try to score in that phase?" said the fullback.