The Atlanta Falcons placed linebacker Sean Weatherspoon on injured reserve-designated to return on Tuesday.
Weatherspoon suffered a foot sprain during Sunday's 31-24 win over the St. Louis Rams.
In two games this season, Weatherspoon has tallied 13 tackles, including 10 solo.
Weatherspoon was selected by the Falcons in the first round (19th overall) of the 2010 NFL Draft out of Missouri. He has complied 306 tackles (218 solo) with eight sacks, two fumble recoveries, one forced fumble and 13 passes defensed in three-plus seasons in Atlanta.
The Falcons added a pair of veteran linebackers in an attempt to offset Weatherspoon's loss, signing both Jamar Chaney and Omar Gaither.
Chaney started 23 games, including all 16 in 2011, over three seasons with Philadelphia, but was released by the Eagles in August. The 26-year-old recorded 24 tackles and one pass defensed in 14 contests, while making five starts, last year.
Gaither owns seven years of NFL experience and appeared in seven games with four starts for Oakland last season, finishing with 14 tackles. He was let go by the Raiders during final preseason cuts.
Atlanta also promoted fullback Patrick DiMarco from the practice squad to replace Bradie Ewing, who sustained a season-ending shoulder separation against the Rams and was placed on IR Monday.