Real Madrid have confirmed that Cristiano Ronaldo has a thigh-muscle strain but have not indicated whether he is likely to be fit in time for Tuesday's Champions League semifinal first leg at Manchester City.
Ronaldo picked up the problem late in Wednesday's 3-0 La Liga win at home to Villarreal when he hurt the muscle attempting an acrobatic bicycle kick and immediately left the pitch even though Madrid had already used all three substitutes.
After the game, Blancos coach Zinedine Zidane suggested the problem was just a scare, and Ronaldo also used social media to play down the issue.
However, tests carried out in the Spanish capital have found a thigh strain that means Ronaldo is likely to miss Saturday's La Liga game at Rayo Vallecano and could be a doubt for Tuesday's Champions League match away to City.
A club statement read: "Following tests carried out today on Cristiano Ronaldo, he has been diagnosed with a muscle strain in his right thigh. His recovery will continue to be assessed."
Madrid are currently one point behind joint leaders Barcelona and Atletico Madrid in La Liga, with all teams having just four games left to play.
Ronaldo, 31, has started every La Liga and Champions League game for Madrid this season and is leading the European Golden Shoe top-scorer race with 31 league goals this season.
Sergio Ramos has suggested that Ronaldo has failed to rest sufficiently because he wants to finish as top scorer.
Real's only other injury concern ahead of Tuesday's game, and the second leg at the Bernabeu the following Wednesday, is an ankle knock for right-back Dani Carvajal.