The LaLiga champion expects to be without Dembele for around five weeks.
"A medical examination on Ousmane Dembele has diagnosed a strain of his left hamstring," a club statement read.
"The Frenchman is set to be out for approximately five weeks as a result."
Dembele, 22, completed 90 minutes as Barca began their title defence with a 1-0 loss at Athletic Bilbao last Friday but has suffered wretched luck with injuries since moving to Camp Nou from Borussia Dortmund in 2017.
The €105million winger sat out most of the first half of his debut campaign in Catalonia due to a serious hamstring injury and this is now the fourth time he has been ruled out by a similar complaint.
Barcelona was without Lionel Messi against Athletic as the superstar forward steps up his recovery form a calf problem, while Dembele's compatriot Antoine Griezmann drew a blank on his Blaugrana debut.
Ernesto Valverde's side entertain Real Betis in the league this weekend.