NFL Network Insider Ian Rapoport reported that Stafford is dealing with tiny fractures in the transverse process of his back, similar to what Tony Romo had several years ago.
The Lions held Stafford out last game and termed the injury day-to-day, but missing two practices to start this week is never a good sign.
Here are other injuries we're tracking on Thursday:
The Steelers inactives for Thursday night's game are: quarterback Paxton Lynch, running back Benny Snell, cornerback Justin Layne, linebacker Anthony Chickillo, offensive tackle Chukwuma Okorafor, tight endZach Gentry and defensive end L.T. Walton.
The Browns inactives for Thursday night's game are: defensive end Olivier Vernon, offensive tackle Kendall Lamm, wide receiver Taywan Taylor, defensive back Eric Murray, defensive back Robert Jackson, offensive lineman Drew Forbes and defensive end Bryan Cox.
»Philadelphia Eagles tackle Jason Peters (knee) and running back Jordan Howard (shoulder) were limited today in practice. Running back Darren Sproles (quad), receiver Alshon Jeffery (ankle) and linebacker Nigel Bradham (ankle) did not participate Thursday.
»Atlanta Falcons quarterback Matt Ryan (ankle) was limited in practice after sitting out Wednesday's session.
Falcons tight end Austin Hooper (knee), running back Devonta Freeman (foot) and safety Kemal Ishmael (concussion) did not practice.
»Carolina Panthers rookie offensive tackle Greg Little cleared concussion protocol. He has not played since Week 3. After missing Wednesday's practice, running back Christian McCaffrey was a full participant at practice Thursday.
»Minnesota Vikings wideout Adam Thielen (hamstring), guard Josh Kline (concussion) and defensive tackle Linval Joseph (knee) did not practice Thursday.
Vikings safety Andrew Sendejo (groin) was limited. Cornerback Xavier Rhodes (elbow), fullback C.J. Hamm (ankle), cornerbacks Mackensie Alexander (groin) and Trae Waynes (ankle) were all full participants in practice.
»Indianapolis Colts quarterback Jacoby Brissett (knee), linebacker Darius Leonard (abdomen) and safety Clayton Geathers (rest) were all full participants in practice. Receiver T.Y. Hilton (calf) and safety Malik Hooker (knee) did not practice. Tight end Jack Doyle (shoulder) was limited.
»New England Patriots safety Nate Ebner (ankle/back) did not participate in practice. Safety Patrick Chung (heel/chest), tight end Matt LaCosse (knee), defensive tackle Danny Shelton (ankle) and defensive end John Simon (elbow) were all limited Thursday.
»Washington Redskins running back Adrian Peterson (toe) did not practice after being limited on Wednesday. Cornerback Josh Norman (hamstring) was a full participant after being limited Wednesday.
»The New York Jets have 23 players listed on the injury report. Here are the notable injuries: running back Le'Veon Bell (ribs/knee/illness), receiver Robby Anderson (back/shoulder), offensive lineman Kelvin Beachum (ankle), receiver Demaryius Thomas, linebacker C.J. Mosley (groin) and offensive lineman Ryan Kalil (knee) did not practice.
»Tampa Bay Buccaneers cornerback Carlton Davis (hip) and linebacker Carl Nassib (groin) were limited participants. Linebacker Anthony Nelson (hamstring) and cornerback M.J. Stewart did not practice.
»Los Angeles Chargers starting tackles Russell Okung (groin) and Sam Tevi (knee) did not practice Thursday.
»San Francisco 49ers tight end George Kittle (knee/ankle), running backs Matt Breida (ankle) and Tevin Coleman (not injury related), kicker Robbie Gould (right quadricep), wide receive Emmanuel Sanders (ribs) and offensive lineman Joe Staley (finger) were all non-participants in Thursday practice. Defensive end Dee Ford (quad), receiver Dante Pettis (back) and running back Raheem Mostert (knee) were limited.
»Arizona Cardinals pass rusher Terrell Suggs (hamstring/back) and running back Chase Edmonds (hamstring) did not practice on Thursday, while cornerback Patrick Peterson (calf) was limited.
»Chicago Bears running back David Montgomery (ankle), linebacker Danny Trevathan (elbow) and tight end Trey Burton (calf) were non-participants in Thursday's practice.
»Oakland Raiders running back Josh Jacobs (shoulder) was limited in practice on Thursday, as were offensive tackle Trent Brown (knee) and center Rodney Hudson (ankle).
»Cincinnati Bengals defensive tackle Geno Atkins (knee) did not practice on Thursday. Wide receiverA.J. Green (ankle) did not practice for the second straight day.