Falcons starting linebacker Sean Weatherspoon will miss at least eight weeks with a foot injury after the team placed him on the short-term injured reserve list today. Weatherspoon suffered the injury during game Sunday against the Rams.

Also, NFL.com reported starting running back Steven Jackson could miss up to four weeks with a thigh injury he suffered Sunday. Falcons coach Mike Smith ruled out Jackson for Sunday’s game at Miami but would not discuss a timetable for Jackson’s return except to say it’s a “short-term” injury.

“I don’t know if that’s two or three weeks,” Smith said today.

That makes four Falcons starters who suffered serious injuries in the game. Linebacker/defensive end Kroy Biermann (Achilles) and fullback Bradie Ewing (shoulder) were ruled out for the season on Tuesday.

To fill the three open spots on the active roster, the Falcons signed fullback Patrick DiMarco from their practice squad and signed free agent linebackers Jamar Chaney and Omar Gaither. The team also signed linebacker Chase Thomas to the practice squad.