Ousmane Dembele was forced off with injury during Barcelona's clash with Leganes on Sunday.
The Frenchman put on a star showing against the Madrid side, and opened the scoring with a smart right-footed finish in the 32nd minute. However, his evening was cut short after he fell awkwardly during the second half.
Ernesto Valverde took the 21-year-old off in the 68th minute, replacing him with Malcom.
The club confirmed after the match that the injury was a sprained ankle and he would be evaluated further on Monday.
A club statement read: "Tests carried out on first-team player Ousmane Dembele have confirmed a sprained ankle that will keep him out of action for approximately 15 days."
Dembele is thus expected to miss both legs of the Copa del Rey quarter-final against Sevilla and LaLiga clashes with Girona and Valencia.
Dembele has been involved in 11 goals in 19 league appearances this season, scoring eight and providing three assists.
Meanwhile, Leganes have sought clarification from the Royal Spanish Football Federation (RFEF) and the Technical Committee of Referees (CTA) regarding Luis Suarez's pivotal second goal in Sunday's match.
Suarez challenged Ivan Cuellar for the ball, meeting it on the volley to restore Barca's lead as the visiting goalkeeper tried to gather.
Leganes believe the incident should have been ruled as a foul against Cuellar and want an explanation over why the goal was not overturned by a VAR review.