Anthony Castonzo has MCL sprain

INDIANAPOLIS -- Indianapolis Colts quarterback Andrew Luck won't have the player responsible for protecting his blindside until Week 1 of the regular season, at the earliest.

Left tackle Anthony Castonzo is out with a mild sprain of the medial collateral ligament in his left knee, an MRI confirmed. The injury happened on the Colts' first offensive series against the Cleveland Browns on Saturday.

"You never want to lose anybody, particularly the guy that's protecting the blindside of your quarterback," Colts coach Chuck Pagano said on a conference call with reporters Sunday.

The Colts are hopeful Castonzo will be ready for the Sept. 8 season opener against the Oakland Raiders.

Joe Reitz will start at left tackle in the Colts' preseason finale against the Cincinnati Bengals on Thursday.

Pagano also said during the conference call that backup receiver Nathan Palmer suffered a sprained MCL against the Browns. Palmer is expected to be out four to six weeks.

Linebacker Lawrence Sidbury was placed on injured reserve Sunday with a shoulder injury, which happened in the Aug. 18 preseason game against the New York Giants.