The thin air in Denver isn't as much of a concern to the Pittsburgh Steelers as their rapidly thinning defensive line.

The Steelers already were without defensive end Aaron Smith, a premier run-stopper who is out for the season with a torn right rotator cuff. Now his backup is hurt, too -- Travis Kirschke has a torn left calf muscle that could sideline him another two weeks. He was injured during the a 27-17 victory over Minnesota on Oct. 25.

One of the strengths of Pittsburgh's traditionally rugged defense is its depth, but that's gone now that Smith and Kirschke are hurt.

Two of the Steelers' least-experienced players, rookie defensive ends Ziggy Hood and Sunny Harris, likely will see meaningful playing time Monday night in Denver.

(Copyright 2009 by The Associated Press. All Rights Reserved.)