Stafford was evaluated in the sideline tent before going to the locker room after his head hit the leg of a Vikings defender during Sunday's game at Minnesota, Dave Birkett of the Detroit Free Press reports.
Stafford was sacked on the play, and afterward officials directed him to the sideline to undergo testing. After his departure, the Lions confirmed that he's being examined for a concussion, which would place him in the protocol for head injuries if he's diagnosed with one. If he's unable to reenter the contest, Stafford will end Week 9 having completed 23 of 32 passes for 211 yards, one touchdown and two interceptions.