The 31-year-old Spaniard picked up the injury in training though manager Arsene Wenger is still to discover the full extent of the problem.
“It could be as long as six weeks, but we don’t know yet,” he said. “We have to check the severity with the doctor.”
Thomas Vermaelen and Nacho Monreal both have back problems and will also miss the season opener against Aston Villa.
However, both forward Theo Walcott (knee) and midfielder Aaron Ramsey (ankle) could feature in Saturday’s match.