The France international joined the Catalan giants as a then club record £96.8m signing at the start of the season but spent several months on the sidelines after picking up a hamstring injury.
Dembele then returned with aplomb in January but has seen his comeback halted after suffering another setback in the 4-2 win over Real Sociedad at the weekend, although Barca insist it is not a recurrence of his previous injury.
A Barcelona statement read: "Tests have confirmed the player has suffered a hamstring injury of the semitendinosus muscle that does not affect the area operated on earlier in the season.
"The injury will mean he will be out for a period of around three to four weeks."
