The Cowboys placed Carter on injured reserve because of a dislocated left elbow suffered on Thanksgiving against Washington and signed Brady Poppinga.
Carter is scheduled to have surgery this week. Lee was placed on injured reserve on Oct. 24 after undergoing right big toe surgery.
Cornerback Orlando Scandrick remains on the active roster despite undergoing left hand surgery on Friday.
Poppinga worked out for the Cowboys in late October when the team signed Gary Guyton. Ernie Sims likely will be promoted to the starting lineup in Carter's absence. Poppinga is an eight-year veteran, spending six years with Green Bay and starting 12 games for St. Louis in 2011.
Poppinga says he tried to keep himself in "Batman" shape -- ready when called -- while sitting out this season. He last played in the 2011 finale with St. Louis.
Armstrong caught three passes in five games for 12 yards earlier this year for Miami. He spent the 2010-11 seasons with Washington and has 54 catches for 986 yards and five touchdowns in his career.
In addition, the Cowboys signed Reggie Jones to the practice squad to replace Danny Coale, who tore an anterior cruciate ligament two weeks ago.
Information from The Associated Press was used in this report.