The Spain international was substituted at halftime during Tuesday's 3-0 Champions League victory over Aston Villa after feeling muscle discomfort.
"The tests have confirmed a minor injury to his right hamstring (biceps femoris muscle)," Barcelona said, adding that his return timeline would depend on his recovery progress.
The injury is a blow to Barcelona ahead of Sunday's top-of-the-table clash, with Hansi Flick's side leading second-placed Atletico by two points.