Real Madrid have confirmed Gareth Bale has muscle damage in his left calf but have put no timescale on the forward's return.
Bale came off in the first half of Real's 4-0 Champions League victory over Shakhtar Donetsk on Tuesday and had a scan in Madrid on Thursday morning.
"Following the tests carried out on Gareth Bale today in the Sanitas La Moraleja University Hospital, the player has been diagnosed with a soleus muscle injury in his left leg," a statement on the official Real Madrid website read on Thursday.
"His condition will be evaluated."
Wales are sweating on Bale's fitness as they need one point from their final Euro 2016 qualifying double-header in October to end a 58-year wait to play at a major tournament.
Chris Coleman's men need a draw against either Bosnia-Herzegovina on October 10 or Andorra three days later to qualify for next summer's European Championship finals in France.
With James Rodriguez already on the sidelines, Real boss Rafa Benitez will also be worried over the 26-year-old's condition, especially with Bale excelling in a more central role for the 10-time European champions.