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.
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.