(CBS) As was feared, the Bears will be without one defensive starter and perhaps more on Thanksgiving Day.

Chicago linebacker Lance Briggs has been ruled out of Thursday’s game at Detroit with a groin injury that he suffered Sunday in a win against Tampa Bay. The Bears have yet to say just how serious Briggs’ injury is, but some have wondered and worried that it could be season-ending.

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In addition to Briggs, linebacker Darryl Sharpton (hamstring) and receiver/returner Chris Williams (hamstring) have also been ruled out. Offensive lineman Brian de la Puente will also be out after being placed on the season-ending injured reserve with an ankle injury.

In his place, defensive tackle Brandon Dunn has been elevated from the practice squad to the 53-man roster. Dunn’s spent the entire season on the Bears’ practice squad after being undrafted out of Louisville.

Defensive tackle Jeremiah Ratliff (knee) and defensive end Trevor Scott (knee) are listed as doubtful. Rookie Will Sutton will likely start if Ratliff can’t play.

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Cornerback Kyle Fuller (knee) is questionable. His absence would be a big blow for Chicago, which has to contend with big-play receiver Calvin Johnson. Al Louis-Jean would have a bigger role if Fuller can’t play.

Receiver Brandon Marshall (ankle), offensive lineman Eben Britton (illness), offensive tackle Jordan Mills (ribs) and safety Brock Vereen (shoulder) are listed as probable.

With de la Puente’s season now over like that of original starting left guard Matt Slauson, the versatile Michael Ola is expected to start at left guard.

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The Bears didn’t practice Wednesday.