The Panthers are placing Thornton (fibula) on injured reserve Wednesday, Mike Kaye of The Charlotte Observer reports.
Thornton suffered a season-ending broken fibula during Monday's loss to the 49ers. The undrafted rookie out of Louisville appeared in 12 regular-season games with Carolina, in which span he played 95 snaps on defense and 83 snaps on special teams and recorded 14 tackles (eight solo), three passes defensed and one forced fumble.