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.
OCT 30 Seth Schwartz
From the NFL to the CFL to the WFL and the USFL, Johnnie Walton's career was one for the ages.
OCT 28 Jeff Fedotin
Hated on by fans, San Diego’s quarterback is having an MVP-caliber year.
OCT 26 Joel Corry
The Tampa Bay defensive tackle cashes in for $95.2 million.