INDIANAPOLIS (AP) -- Colts coach Chuck Pagano said left guard Donald Thomas has torn a quad tendon in his right leg and will probably miss the rest of the season.
Pagano said Thomas will need to have surgery on the leg.
It's yet another big blow for a team that also lost starting running back Vick Ballard this week with a torn anterior cruciate ligament in his right knee.
Thomas was expected to play a major role in Indy's revamped offensive line. He was one of Indy's first free-agent signings in March and was immediately installed as the starter on the left side of a line that was being beefed up to create bigger running lanes and more protection for Andrew Luck.
He was replaced Sunday by rookie draft pick Hugh Thornton, who will probably keep the job through this season.
It wasn't entirely clear what led to Thomas' injury, though he wound up on the ground and was grasping at his right knee after Luck completed a 22-yard pass to T.Y. Hilton down the right sideline. Thomas stayed on the ground for before being taken off the field on a cart.
AP NFL website: www.pro32.ap.org