Colts left guard Donald Thomas will have season-ending surgery in the next few days and will be put on injured reserve.
Coach Chuck Pagano made the announcement Monday.
Rookie Hugh Thornton, a third-round draft pick, replaced Thomas during Sunday's 24-20 loss to Miami and is expected to make his first NFL start this weekend at San Francisco.
It was a tough week for the Colts (1-1), who lost starting running back Vick Ballard when he tore the anterior cruciate ligament in his right knee during Thursday's practice. Tight end Dwayne Allen (hip) was inactive for Sunday's game, and receiver Darrius Heyward-Bey left Sunday's game with what was initially described as a rib injury.
Amid all that, the Colts lost their first home game in 12 months, too.
AP NFL website: www.pro32.ap.org