After the 31-year-old was ruled out of last week's game against the Chicago Bears with fractured bones in his back -- the team and sources originally said they believed it to be a week-to-week injury.
"We deactivated him this morning," Lions general manager Bob Quinn said last Sunday, as ESPN reported. "Had the back injury last week near the end of the Oakland game. Practiced on limited all week, listed him as questionable. Got to the stadium this morning, met with the doctors and wasn't medically cleared to play today so he's deactivated. So that's it."
On Friday, the team officially ruled him out of Sunday's game against the Dallas Cowboys, his second consecutive missed start. Lions head coach Matt Patricia had called the injury "day to day" and "week to week."
Doctors have since told Stafford he's dealing with "a six-week injury," sources told ESPN.
They added the QB could return sooner.
"This doesn't mean Stafford will be sidelined six games, but it does provide a glimpse into the severity of the injury that he has played through before the Lions' doctors denied him from playing last week against the Chicago Bears and Sunday against the Dallas Cowboys," ESPN's Adam Schefter said, citing a source.
Stafford started 136 consecutive games for the Lions before missing last week's contest. It was the second-longest active start streak for a quarterback in the NFL behind Philip Rivers.
It was also the 6th longest all-time start streak for a QB, behind Brett Favre, Rivers, Eli Manning, Peyton Manning and Matt Ryan.
The next closest was Joe Flacco with 122 consecutive starts.
Jeff Driskel is set to replace Stafford again for his seventh career start -- after he completed 58 percent of his passes for 269 yards in a 20-13 loss against the Bears last Sunday.