Barcelona have revealed that Ousmane Dembele will undergo surgery on Tuesday after rupturing a tendon in his thigh in Saturday's 2-1 win against Getafe.
The club's record signing was forced to withdraw in the first half of the game with what at first appeared to be a less severe hamstring pull.
But he is now set to miss up to four months of the season, and will have an operation in Finland on Tuesday.
A statement on the club's website read: "First team player Ousmane Dembélé travelled on Monday morning to Helsinki, Finland, where he will undergo surgery to repair a rupture of the biceps femoris tendon in his left thigh.
"Dembélé was accompanied by team physician, Dr. Ricard Pruna. Dembélé will be operated on Tuesday by Dr. Sakari Orava. Following the surgery, the Club will provide a medical statement.
"Dembélé was injured on Saturday at the Coliseum Alfonso Pérez in the league match against Getafe and had to be replaced on 28 minutes by Gerard Deulofeu.
"According to the medical announcement that the Club made public this Sunday, Dembélé will be out of action for three-and-a-half to four months."
Barcelona signed Dembele from Borussia Dortmund for an initial €105m, although it could rise to €145m with add-ons.
The youngster made his debut as a substitute in last weekend's 5-0 victory over Espanyol, providing an assist for Luis Suarez.
He then made his first start in Tuesday night's Champions League opener against Serie A champions Juventus.