Gareth Bale is out of Real Madrid's UEFA Champions League clash with Copenhagen on Wednesday after missing training with his team-mates on Tuesday.
The Welshman had instead taken part in an individual session in the gym, but he has been left out of coach Carlo Ancelotti's 21-man squad for the game against the Danish champions.
"Gareth Bale has not trained with the group due to muscular problems in his left thigh," said a statement on the club's official website. "The diagnosis is dependent upon tests which will be carried out tomorrow."
The 24-year-old also missed league games against Getafe and Elche last week due to a left thigh problem. However, he returned to make his home debut as a second-half substitute in the 1-0 defeat to Atletico Madrid on Saturday.
That defeat left Real already five points behind Atletico and Barcelona, who have both made 100 per cent starts to La Liga after seven games. And Ancelotti said he expects a reaction from his players upon their return to Champions League duty.
"I'm less happy after the game against Atletico because it wasn't good, losing a derby is never a good thing," he told a press conference on Tuesday.
"We need to react quickly, both in terms of our performance and results. I have confidence in the players that they will respond well. It is a question of spirit and attitude."