The Washington Redskins arrived at training camp last month with questions about their offensive line, with two starters — left guard Kory Lichtensteiger and right tackle Jammal Brown — returning from injuries from last season and relatively little having been done in the offseason to fortify the group.

   Now as the four-game preseason nears, the questions are even bigger. Brown and Lichtensteiger again are sidelined. Brown aggravated his hip injury running sprints on the day before camp began and remains on the physically unable to perform list. Lichtensteiger underwent arthroscopic knee surgery.

   Right guard Chris Chester joined them on the shelf, at least temporarily, when he suffered a sprained ankle during Monday’s practice.

Coach Mike Shanahan described Chester’s ankle sprain as mild and said he hopes Chester can return to the field within a few days. But the Redskins finished Monday’s practice with three backups working with the starting offensive line. Tyler Polumbus has been filling in at right tackle. Maurice Hurt has been practicing at left guard. Adam Gettis replaced Chester at right guard, with only left tackle Trent Williams and center Will Montgomery left unhurt from the originally projected starters.

   The Redskins open the preseason Thursday night at Buffalo and it’s not clear if Chester will play. But neither Brown nor Lichtensteiger is close to returning at this point. Shanahan has said he hopes to have Lichtensteiger in the lineup for the regular season opener at New Orleans next month but doesn’t plan to risk having him play before then. No timetable has been given for a return by Brown.

   The Redskins have signed two veteran offensive linemen with NFL starting experience, tackle Jordan Black and guard Tony Moll, since training camp began. But neither is pushing for a starting job at the moment. Black is trying to put on weight after being out of the league last season. Moll has not been eligible to participate in contact drills yet under a provision in the collective bargaining agreement.

   The mobility of rookie quarterback Robert Griffin III should help the offensive line. But the unit’s performance Thursday night will be under great scrutiny during the 12 to 20 snaps that the starting offense is scheduled to be on the field, and concerns about the patchwork offensive line’s ability to protect Griffin could intensify if there are struggles against the Bills.