FLOWERY BRANCH, Ga. (AP) -- Atlanta has lost linebacker Sean Weatherspoon for at least eight weeks and running back Steven Jackson will miss the Falcons' next game - and maybe more.
The win against St. Louis Sunday is proving to be costly.
Weatherspoon became the third starter placed on injured reserve Tuesday after the victory over the Rams, though he will be eligible to rejoin the roster in Week 11.
The Falcons (1-1) used the one-time-only designation that allows an injured player to return, but Weatherspoon won't be able to practice for six weeks and can't play in a game for eight weeks.
Coach Mike Smith announced Jackson will miss Sunday's game at Miami with a thigh injury.
Smith said Jackson's injury is not expected to keep him out for a significant amount of time.
''He will not play this week. I know that,'' Smith said. ''It is short term. When I say short term, I don't know if it's two weeks or three weeks, but Steven is ruled out for the game this week and will not play.''
Smith provided no further details on Jackson's injury.
The announcement came one day after the Falcons placed defensive end Kroy Biermann (torn right Achilles tendon) and fullback Bradie Ewing (separated left shoulder) on the reserve list with season-ending injuries.
Smith said he hasn't experienced a similar wave of injuries in his six years as Atlanta's coach.
''We've not had anything close to this,'' Smith said. ''There have been games where we've had guys who have not been able to play and it's been the next-man up mentality and I think that's really what our guys understand. I tell them all the time we have very defined roles on our team and in our organization, but I tell them on our team those roles can change just like that and you've got to be prepared.''
Asked if the injuries have left his head spinning, Smith said ''No. Not at all.
''That's what happens week to week. ... I think it happens at different times of the season. Right now it's happening at the beginning of the season.''
Jackson left the 31-24 win over the Rams after scoring in the first quarter on an 8-yard pass from Matt Ryan. Smith says Jacquizz Rodgers and Jason Snelling will share the work at running back against the Dolphins.
The status of cornerback Asante Samuel also is in doubt. Samuel left the game against the Rams with a thigh injury.
Weatherspoon, a first-round pick in 2010, quickly established himself as the leader of Atlanta's defense. He had 13 tackles this season and 306 in his career. Biermann has 16 1/2 sacks in his career, including four last season, and took on the expanded role of outside linebacker when the Falcons went to a 3-4 alignment.
Replacing Weatherspoon is particularly troublesome, however, because linebacker is the team's thinnest position. There were only four other linebackers on the roster, including two undrafted rookies, before the Falcons signed Jamar Chaney and Omar Gaither on Tuesday.
Smith said the two undrafted rookies, Joplo Bartu and Paul Worrilow, will play significant roles. Bartu started ahead of Stephen Nicholas against the Rams.
''We're looking forward to seeing what these young guys can do,'' Smith said. ''Bartu had a good ballgame last week and Worrilow and Nicholas are guys that get back into the mix. They've got to go out there and perform and we're very confident that they will.
''The two young guys showed what they can do in the preseason and then Bartu did it in the game the other day.''
Chaney, a seventh-round pick by Philadelphia in 2010, played 44 games with the Eagles over the last three seasons, including 23 starts. Gaither also is a former Eagles draft pick, spending five years in Philadelphia before moving to Carolina in 2011 and Oakland last season. He played in seven games with four starts for the Raiders.
The Falcons have greater numbers at defensive end, but getting pressure on the quarterback has been a long-standing trouble spot and there's no one else in a backup role with even Biermann's modest credentials.
Jonathan Massaquoi filled in after Biermann's injury against the Rams. The Falcons also have rookie draft picks Malliciah Goodman and Stansly Maponga at defensive end.
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