Barcelona have confirmed that club-record signing Ousmane Dembele will be sidelined for up to four months after rupturing a tendon in Saturday's win at Getafe.
Dembele, 20, will travel to Finland this week to undergo surgery with a specialist.
The France international was making his first ever La Liga start at the Coliseum Alfonso Perez when he was forced off after just 25 minutes.
The Catalan club had initially hoped he had suffered a minor hamstring problem and would only be out for a few weeks, but tests at the club's training ground on Sunday revealed the worst case scenario.
"Tests have confirmed that first team player Ousmane Dembele has ruptured the tendon in his femoral bicep in his left thigh," Barca said in a statement.
"The player will be operated on by Dr. Sakari Orava in Finland this week. He is expected to be out for between three and a half months and four months."
After Neymar left for Paris Saint-Germain for €222 million, Barca used some of the money to sign Dembele from Borussia Dortmund, with the former Rennes forward replacing Luis Suarez as the club's most expensive ever signing.
Barca paid an initial fee of €105m for Dembele, although that could eventually increase to €145m with add-ons.
Dembele made his debut for Barca as a substitute in last weekend's Catalan derby win over Espanyol, setting up the fifth goal for Luis Suarez.
Barca boss Ernesto Valverde then handed him his first start in the Champions League victory over Juventus in midweek.
However, after rupturing a tendon in his full La Liga debut at Getafe, he is unlikely to play for the club again until the New Year.
Barca, therefore, will be without him for the remainder of the Champions League group stages, while it is also likely he will miss the first league Clasico of the season against Real Madrid, which is scheduled for Dec. 23.
Dembele's injury represents an opportunity for another summer signing, Gerard Deulofeu, to stake his place for a regular first-team place.
Deulofeu re-joined Barca from Everton this summer for €12m and until the arrival of Dembele had been Valverde's preferred option in attack with Lionel Messi and Suarez.
Other options include Paco Alcacer, Denis Suarez and Arda Turan, who remains at the club after a move to Galatasaray fell through at the last minute earlier this month.
However, none of the alternative options offer the same pace and width as Dembele, which is something Valverde had stressed he was keen to add to the squad following the loss of Neymar to PSG in August.