It's unclear how Stafford incurred the injury, though he did take a hard shot against the Raiders in a last-second loss last Sunday. He was limited all week, but publicly there did not seem to be concern.
"Had the back injury last week near the end of the Oakland game," Lions general manager Bob Quinn said in a statement before Sunday's game. "Practiced on limited all week. Listed him as questionable. Got to the stadium this morning, met with the doctors, and he wasn't medically cleared to play today. So, he's deactivated."
Asked about his status by local reporters on Wednesday, Stafford said, "I'm fine."
"I'll be good to go," Stafford said. "I'm not really worried about it. Something different, but I'm totally good."
The injury is brutal for Detroit and Stafford, who is having one of the best seasons of his career. He's averaging 312.4 passing yards per game and has a career-high passer rating of 106. Now, at least for one game, they'll be without him.