Xavier Adibi is a four-year veteran, logging action in 38 games with eight starts. He has 55 tackles, two forced fumbles and one fumble recovery to his name on defense and on special teams has recorded 13 tackles. He spent last season with the Vikings after being drafted in the fourth round by the Texans and spending three years with them.
K.C. Asiodu is a two-year veteran who spent 2009 with the Rams (playing in 10 games) and 2010 with the Saints (one game). He's recorded nine special teams tackles but no significant action on defense.
In addition to Urlacher's issues, Dom DeCicco and Jabara Williams are both nicked up and unable to practice.
Aston Whiteside is everything you'd find in a Jerry Angelo draft pick or last year's free agency - an undrafted rookie defensive end (who's versatile enough to play linebacker) that initially signed with the Cowboys and is a product of Abilene Christian. I couldn't find anything about an injury history, though.
To make room on the roster, undrafted free agent defensive tackle Ronnie Cameron and cornerback Jeremy Ware were waived.