Mascherano out for up to two weeks
Barcelona's Javier Mascherano takes part in a training session in Sant Joan Despi, near Barcelona, on August 17, 2013.
The Argentine international limped off after just 35 minutes of Barca's 4-1 win over Real Sociedad on Tuesday night and tests carried out on Wednesday confirmed that he will be out for up to two weeks.
"Tests realised this morning have confirmed that the hamstring strain will force him out for 10 to 15 days," said a statement on Barca's website.
Mascherano will therefore miss Saturday's trip to Almeria as well as the meeting with Celtic and probably the home match against Valladolid on October 5.
His absence leaves Barca boss Gerardo Martino extremely short of cover in central defence with Gerard Pique the only established fully-fit centre back available.
Twenty-two-year-old Marc Bartra replaced Mascherano on Tuesday and scored Barca's fourth goal but is relatively untried, whilst captain Carles Puyol is still working his way back to match fitness following knee surgery in March.
Brazilian full-back Adriano also deputised at centre-back last season, but he is currently filling in for Jordi Alba at left-back as the Spanish international is also sidelined with a hamstring injury.