Atletico Madrid left-back Filipe Luis suffered a spasm in his left hamstring during Wednesday's Champions League win over PSV, the club confirmed.
The Brazil international was forced off in the 72nd minute and replaced by Juanfran after pulling up with the injury.
Filipe Luis limped off clutching the back of his leg and medical examinations afterwards revealed that he suffered a spasm in his semitendinosus muscle, one of the hamstrings located in the back of the thigh.
Atletico's medical staff are yet to determine the seriousness of the issue, though.
A statement from the club read: "After a first exploration by the club's medical services, we have found that our left-back Filipe Luis suffered a muscle spasm in the semitendinosus muscle in the back of the left thigh.
"The Brazilian was substituted after 72 minutes by Juanfran Torres and the full extent [of the injury] is still pending."