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 after sustaining the injury in second half stoppage time.
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 table, seven points adrift of joint leaders Atletico Madrid and Real Madrid.
The Camp Nou outfit’s start to the current campaign is their worst since 2003. With seven wins from their first 15 matches, it is the first time they have failed to win more than half of their games at this stage in the season since Frank Rijkaard was at the helm. Barca finished second in the league that season, five points behind champions Valencia.
After the latest slip up, coach Koeman admitted his side will struggle to get back into the race for the league title.
He said in a press conference: "I am realistic, it will be very difficult to be champions. Nothing is impossible, but you have to acknowledge the gap. Atletico look very good to me, very strong, they don't concede many goals."
The Catalan side begin 2021 with an away match against Huesca on Sunday, with a trip to Athletic Club to follow three days later.