Barcelona playmaker Philippe Coutinho will undergo arthroscopic surgery to determine the severity of an injury to his left knee.
The Brazil international was introduced as a 66th-minute substitute during Tuesday's disappointing 1-1 draw with Eibar at Camp Nou but was unable to see the game out.
Initial reports suggested Coutinho could be facing a lengthy spell on the sidelines and the club confirmed on Wednesday he had damaged a lateral meniscus and will now have an exploratory operation.
A Barcelona statement read: "The tests carried out on the first team player Philippe Coutinho have shown that the midfielder has an injury to the lateral meniscus in his left knee. Treatment will necessitate arthroscopic surgery which will take place in the coming days."
A lengthy absence for Coutinho would be another blow for Barca boss Ronald Koeman, who is already without Ansu Fati, Sergi Roberto and Gerard Pique through injury.
Coutinho has made 14 appearances for Barcelona this season in all competitions, with three goals and two assists.
The draw with Eibar saw the Catalans slip to sixth in the LaLiga table, seven points adrift of joint leaders Atletico Madrid and Real Madrid.