Colts left guard Donald Thomas will require season-ending surgery to repair his injured right quad.
Coach Chuck Pagano said Thursday an MRI confirmed the diagnosis.
Thomas also missed most of last season with a torn right quad in Week 2. The Colts also said he had offseason surgery to repair a torn biceps.
Indy thought Thomas' return would solidify an offensive line that couldn't stay healthy in 2013, struggled to open running lanes and allowed franchise quarterback Andrew Luck to be hit far too many times. Rookie Jack Mewhort, Indy's second-round pick, and NFL veteran Lance Louis will now compete for the open job.
Thomas, running back Vick Ballard and defensive lineman Fili Moala are all out for the season.
AP NFL website: www.pro32.ap.org and www.twitter.com/AP_NFL