Cornerback Marlin Jackson and strong safety Bob Sanders were lost for the season Friday when the team placed them on injured reserve.
Jackson, who missed the second half of the 2008 season after injuring his right knee during practice, suffered an anterior cruciate ligament injury to his left knee during a non-contact drill Wednesday. He had been rehabbing the knee after he was hurt against Seattle on Oct. 4.
Sanders had just returned to the Colts' lineup two weeks ago. He had missed all of training camp and the first five games of the year after undergoing offseason knee surgery. He has missed 40 of 87 games during his injury-plagued, six-year NFL career.
Indianapolis' other veteran cornerback, Kelvin Hayden, is also expected to be sidelined for the next three to four weeks after he suffered a sprained knee during the 18-14 win over San Francisco. Hayden is not expected to undergo surgery.
"Not real sure (how long Hayden will be out)," coach Jim Caldwell said. "We're kind of looking at probably a three to four week window."
The Colts (7-0) host AFC South rival Houston (5-3) this Sunday. Texans quarterback Matt Schaub and receiver Andre Johnson will likely be looking at the Colts defense which starts two rookie cornerbacks -- Jerraud Powers and Jacob Lacey. Three-year veteran Melvin Bullitt will take Sanders' place at strong safety.
Wide receiver Anthony Gonzalez, meanwhile, underwent arthroscopic surgery Thursday to clean out loose particles in his right knee. Gonzalez suffered a sprained ligament in the knee during the Colts' season-opening win over Jacksonville. A date for his return has yet to be determined.
"(Sanders and Gonzalez) are fine football players, great leaders and members of our team," Caldwell said. "The thing about it, though, we've had young people step up and do a great job in their absence. We'll continue on that path."
Copyright 2009 by The Associated Press