CHICAGO -- The NFL is looking into how the Detroit Lions handled the reporting of quarterback Matthew Stafford's back injury in the week leading up to Sunday's loss to Chicago, including the designation of Stafford as questionable before he was ruled out, a source said.

"We'll look into it and gather all the facts," a league source told ESPN, "as is standard in situations like this."

This isn't the first time in recent memory the league has looked into potential injury report violations. The NFL investigated similar situations regarding Ben Roethlisberger and Pittsburgh earlier this year and the Miami Dolphins with Ryan Tannehill last season.

A message left by ESPN for the Lions was not immediately returned.

Detroit had listed Stafford as limited in practice all week and then listed him as questionable on the injury report Friday. Here's where it then got a little bit dicey. Media reports started to surface Saturday saying Stafford would be a game-time decision. By Sunday morning, those same reports said he would be ruled out -- ending a 136-game starting streak that had been the second-longest active streak among quarterbacks.

Lions general manager Bob Quinn said Sunday that Stafford suffered the injury late in Detroit's Week 9 loss to Oakland. However, a source told ESPN's Adam Schefter the injury dates back to last season, when Stafford played through the pain and didn't miss a game.

Following Sunday's game, multiple players told ESPN and other outlets that they were informed at various points Saturday that Stafford would be unable to play.

"We found out yesterday," Lions left tackle Taylor Decker said Sunday. "It was kind of a surprise. For him to not be out there, we know it's a really serious situation."

Offensive guard Joe Dahl told ESPN on Sunday that the Lions found out "last night, maybe." And tight end Logan Thomas said the team found out Saturday as well.

Stafford's replacement at quarterback Sunday, Jeff Driskel, said he went through a typical week of practice with a "sprinkling" of first-team reps and he was told Sunday he would be the starter.

However, Lions coach Matt Patricia, in his postgame news conference, said the decision was made Sunday that "it was unsafe" for Stafford to play. Schefter reported that Stafford has fractured bones in his back.

"I'm not going to get into too many specifics but he truly was limited. Participated but truly limited through the week and we were hoping by the time we got to today that we were going to be able to do it," Patricia said. "And like I said, it just wasn't safe to put him in that situation. So the information that we got, talking with the doctors, it wasn't the right thing to do. Again, I'm more concerned about him more than anything else. He's got a great family. He's a great guy.

"So for us, that was a decision that we made and we moved forward and the team, you know, they moved forward with the decision and I think a lot of those guys were trying to fight and do everything they could because they know how tough he is and they know how much it means to him and I think they were trying to do everything we could for him. That's it."

Quinn said the Lions "deactivated him" Sunday morning because doctors decided he wasn't medically cleared to play.

The league's typical protocol in this matter is to contact the club and ask for all relevant documents pertaining to the injury and the handling of it. In the league's manual, it states "if, prior to the team's arrival at the stadium on game day, an event occurs that causes the club to decide that a player will not start or will not play, the club must update its Game Status Report, as required by the Policy."

That goes up until the earliest time the team is instructed to report to the stadium on the day of the game. If the decision is made after the team arrives at the stadium and a workout is conducted that decides a player will be unable to start or play, they are not required to change the status report until the typical window 90 minutes before kickoff.