Donald Thomas, who was expected to start at guard this season, re-tore the same quad that cost him all but two games during the 2013 season. He will miss the entire 2014 campaign.
"Donald worked extremely hard to get back. I feel awful for Donald," said Colts coach Chuck Pagano. "He was playing extremely well and doing a great job. Donald will be fine and he'll go back to work to rehab that quad."
Thomas will have surgery on the quad, likely ending any possibility of him playing this season.
Thomas tore the quad late in the Colts' Wednesday afternoon practice. It became obvious that the injury was severe when Thomas finally got up from the ground and threw his helmet in anger.
Rookie Jack Mewhort, the Colts' second-round pick, will likely get the first shot at starting at guard in Thomas' place.
The Colts lost running back Vick Ballard for the season with a torn Achilles on July 25.
Colts G Thomas Suffers Quad Injury
Mike Wells discusses how the loss of Donald Thomas affects the Colts' offense.