Barcelona could lose midfielder Seydou Keita for up to a month because of a hamstring injury, the European champion said on Monday. The Mali ace appeared to have torn a hamstring early in Saturday's 2-1 defeat at Atletico Madrid and is now set for a four-week layoff. Keita's injury adds to Pep Guardiola's woes as Barca already miss Eric Abidal, Yaya Toure, Daniel Alves and Dmytro Chygrynskiy. The 30-year-old is now set to miss next week's Champions League tie at Stuttgart and is doubtful for the return leg in March.