Chicago Bears Pro Bowl defensive tackle Henry Melton, the team's franchise player, suffered a concussion against the Carolina Panthers.
He'll have to pass an NFL baseline neurological test before he can resume playing.
Wide receiver Earl Bennett is also sidelined with a concussion.
"Henry has a concussion and he'll be in a NFL concussion protocol situation right now and will be day-to-day," Bears coach Marc Trestman told reporters.
Melton made the Pro Bowl last season when he finished with six sacks and 33 tackles.
The Bears didn't get anywhere in contract talks with Melton, so he'll play this season under the franchise tag.
Follow me on Twitter: @RavensInsider
Aaron Wilson covers the Ravens for The Baltimore Sun.
Check out our partners at TiqIQ for the best deals on all games on the 2014 NFL schedule.
SEP 23 Jesse Lawrence
Jesse Lawrence of TiqIQ looks at the week ahead
SEP 19 Jeff Fedotin
Jets hold out hope cornerback can bolster beleaguered secondary.
SEP 17 Jesse Lawrence
Jesse Lawrence of TiqIQ takes a look at the hot tickets this weekend.