Cowboys linebacker Bruce Carter is out of for the season with a dislocated left elbow, making him the fourth Dallas defensive starter to go on injured reserve.
Carter injured the elbow in Thursday's 38-31 loss to Washington. The Cowboys have lost both inside linebackers with defensive leader Sean Lee suffering a season-ending toe injury last month.
The other defensive starters out for the year are safety Barry Church and defensive end Kenyon Coleman.
The Cowboys said Monday they filled Carter's roster spot by signing Brady Poppinga, a seven-year veteran who last played for St. Louis in 2011.
Dallas also released receiver Andre Holmes and replaced him with veteran Anthony Armstrong. Miles Austin injured a hip in the Washington game.