Real Madrid said new tests showed Cristiano Ronaldo has sustained a left hamstring injury but did not indicate how much longer the star forward would be out of action.

"Medical tests performed on Cristiano Ronaldo have revealed an injury to the player's left biceps femoris muscle. Pending a medical evaluation," the team said in a brief medical update Thursday on its Web site.

The Portuguese international, who has been struggling in recent weeks with a patellar tendon injury in his left knee, last played on April 2 in the first leg of Real Madrid's quarterfinal Champions League clash against Borussia Dortmund, although he was visibly in discomfort and had to be substituted with 10 minutes left in the contest.

He subsequently missed Los Blancos' Spanish league match last Saturday against Real Sociedad and also missed Tuesday's second leg of the Champions quarterfinal.

The hamstring injury was detected in new tests carried out after Real Madrid squeaked out a 3-2 victory on aggregate over Dortmund.

The injury comes at a critical time for Real Madrid, which will square off against arch-rival FC Barcelona in the Copa del Rey final on April 16 in Valencia and play the first leg of its next Champions League series on April 22.

Los Blancos also are locked in a three-team battle with Atlético Madrid and Barça for this year's Spanish-league crown. Real Madrid is currently in third place but trails league-leading Atlético by just three points with six games to play.

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