Real Madrid forward Gareth Bale limped off with an apparent calf strain in Saturday's La Liga game with Malaga.
The Welshman went down holding his left calf after a challenge just five minutes into the game.
Bale, 25, is now a doubt for Wednesday's Champions League quarter-final, second leg with Atletico Madrid.
He was rested against Eibar last weekend due to muscle fatigue but played in Tuesday's first leg at Atletico Madrid that finished 0-0.
Luka Modric is another doubt for coach Carlo Ancelotti, as the midfielder had to be withdrawn on the hour mark after suffering a heavy blow to his knee.
The Croatian only recently returned from a five-month injury layoff and his presence has coincided with his side's upturn in form in recent weeks.
Karim Benzema also missed the Malaga match with a knee problem but the club are more optimistic that he will be ready to face Atletico.
"At the moment we can't say anything but we will evaluate the situation over the next few days," Ancelotti said after the 3-1 win over Malaga.
"I think that he (Benzema) will be okay (to face Atletico) as he is improving. We have several days and he could well recover."