Real Madrid midfielder Gareth Bale damaged a calf muscle in his left leg during Tuesday's 4-0 Champions League Group A victory at home to Shakhtar Donetsk, tests confirmed on Thursday.
The Wales international had to come off in the first half and was replaced by Croatia midfielder Mateo Kovacic.
"Following the tests carried out on Gareth Bale today ... the player has been diagnosed with a soleus muscle injury in his left leg," Real said on their website. "His condition will be evaluated."
Real have La Liga games against Granada, Athletic Bilbao and Malaga before they play at Swedish side Malmo in their second Champions League match of the campaign at the end of the month.
Pedro and Willian out of Arsenal clash
Chelsea will be without Pedro and Willian in Saturday's Premier League clash with Arsenal, manager Jose Mourinho has said.
Mourinho's team have made a stuttering start to their Premier League title defence, managing four points from their five games that leave them fourth from bottom in the league table.
Opponents Arsenal have recovered from their opening day shock defeat to West Ham United to collect 10 points from five games and sit fourth in the table.
Willian, who scored the opener in Chelsea's 4-0 Champions League win against Israeli side Maccabi Tel Aviv on Wednesday, was forced off in the 23rd minute and Pedro didn't feature in the win.
"Tomorrow I will watch Arsenal, and I will try to understand how my players are -- how Oscar is, Willian is out for sure, I think Pedro is out for sure -- so let's see," Mourinho told reporters.
Pedro and Willian have contributed four of the seven league goals Chelsea have scored and they will be sorely missed as the Blues prepare to take on an Arsenal side who have kept three successive clean sheets in the league.