Bass was limited in the session, and a potential absence would further hamper a defensive line that has taken more than its share of injuries.
Defensive end Anthony Spencer has not practiced since July 25 because of left knee surgery and suffered a minor setback over the weekend when his knee swelled after running. Defensive tackle Jay Ratliff is on the physically unable to perform list because of a sports hernia and will miss at least the first six games. Defensive end Tyrone Crawford was hurt in the first training camp practice, tearing his Achilles.
On Sept. 1 the Cowboys traded Sean Lissemore to San Diego.