Ngata injured his knee a week ago in a win over Cincinnati and was able to finish the game. However, he was unable to practice this week.
Without Ngata, the Ravens will likely rotate Terrence Cody and Brandon Williams in at nose tackle.
Also inactive is receiver Marlon Brown, who popped up on the injury report as questionable after missing Friday's practice due to a knee injury.
Here's the full list of inactives:
BEARS INACTIVES: QB Jay Cutler, LB Lance Briggs, LS Patrick Mannelly, DE Shea McClellin, DL Jay Ratliff, OL James Brown, OL Jonathan Scott.