Matt Forte left with a knee injury in the second half of Sunday's 23-20 loss to the Minnesota Vikings.
Forte, 29, walked to the locker room in Chicago under his own power and did not return.
The Bears' running back suffered a big hit in the open field by Minnesota Vikings safety Harrison Smith early in the third quarter.
Forte, the Bears workhorse, earned 41 yards on 10 carries and four receptions for 28 yards before exiting.
Chicago receiver Eddie Royal also exited the game with a knee injury and was ruled out.
Bears coach John Fox told reporters he didn't know the severity of Forte's injury. Jeremy Langford would be next up if Forte misses time. The Bears play on Monday night in Week 9 at San Diego, so Forte has extra time but owners may be forced to wait until game time to know Forte's status.