The France international will have to watch on from the sidelines for a lengthy period after suffering a hamstring injury against Getafe
Ousmane Demeble has been ruled out for up to four months in an injury blow that has rocked Barcelona.
Barca have confirmed that the 20-year-old did, as feared by head coach Ernesto Valverde, suffered a torn hamstring in Saturday's 2-1 victory away against Getafe, which was his full La Liga debut.
Dembele had to be withdrawn in the first half of his side's dramatic win, leaving the field after sustaining the problem while attempting a back-heel near the corner flag when the match was still goalless.
After conducting tests on Sunday, Barca released a statement which read: "The tests have come back following first team player Ousmane Dembele has ruptured the tendon in his femoral bicep in his left thigh.
"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."
The problem, which is in Dembele's left leg, will see him miss the first half of the season in a huge blow to the Catalans after his initial €105million move from Borussia Dortmund.
Barca, who have won all four of their La Liga matches to start the new season, have clashes against Eibar, Girona, Sporting CP and Las Palmas before the next international break.
Dembele is also set to miss huge league fixtures against Atletico Madrid, Sevilla, Valencia and the rest of the Champions League group stages.
The France international is also in line to miss the first league Clasico of the season against Real Madrid in December, with his return coming after the mid-season break.
Dembele had made his first Barca start against Juventus in the Champions League on Tuesday, having come on as a substitute at home to Espanyol last week, his first game in the club's colours.