"Tests which Cristiano Ronaldo underwent have shown up a muscular injury to his left biceps femoris," Real said, adding that his return to action was dependent on his reaction to rehabilitation.

According to the As newspaper website, Ronaldo could be out for two weeks, which would mean him missing the King's Cup final in Valencia on Wednesday as well as the Champions League semi-final, first leg match on April 22-23.

Ronaldo, scorer of 28 league goals this season, didn't play in Real's 4-0 La Liga victory over Real Sociedad on Saturday or Tuesday's 2-0 defeat by Borussia Dortmund in the Champions League quarter-final, second leg, officially because of a left knee injury.

Real, third in La Liga behind city rivals Atletico Madrid and Barcelona, host Almeria on Saturday in league action.

Coach Carlo Ancelotti was handed welcome news, however, after Brazilian left-back Marcelo resumed training on Thursday.

His return comes 10 days after a hamstring injury that ruled him out of the Borussia Dortmund matches.