Lions left tackle Riley Reiff missed practice Tuesday, and all signs point to him not playing in Thursday's game against the Chicago Bears.
Reiff suffered a left knee injury on the first play of Sunday's loss to the New England Patriots and did not return.
On Tuesday, the Lions promoted offensive lineman Rodney Austin from the practice squad to the active roster, a move that gives them an extra backup if Reiff can't play.
A first-round pick in 2012, Reiff has started every game the past two years since Jeff Backus retired. Backus missed just one start in 12 seasons with the Lions, the Thanksgiving game in his final season.
"He's as tough as they come," Lions quarterback Matthew Stafford said of Reiff. "He filled in for a guy that kind of showed him the ropes when it comes to that. Jeff Backus was a bell cow for a long time at left tackle, and Riley's very similar in his personality and his approach to football and what is being hurt and what is not.
"I know that Riley is doing everything he can to get back on the field on Thursday. We'll see if it happens."
Lions coach Jim Caldwell did not have an update on Reiff's status before practice Tuesday.
In addition to Reiff, right guard Larry Warford and defensive tackle Nick Fairley didn't practice Tuesday and remain unlikely to return until at least December.
Linebacker Ashlee Palmer returned to practice Tuesday after suffering a concussion in the first quarter of Sunday's game, but he was limited.
The Lions didn't practice Monday but had to release a projected report. On Monday, wide receiver Calvin Johnson and safety James Ihedigbo were listed as out. Both practiced Tuesday but were limited.
Defensive end Ezekiel Ansah (elbow), running back Reggie Bush (ankle/back), safety Glover Quin (back), cornerback Rashean Mathis (ankle) and defensive end George Johnson (foot) were all limited, too, but they are likely receiving extra rest to be healthy for Thursday.
Still, even with healthy skill position players, the Lions could struggle Thursday if Reiff can't play. With Warford also out, the Lions would likely start two rookies on the line — Travis Swanson at right guard and Cornelius Lucas at left tackle.
However, the good news is the Lions don't expect Reiff's injury to be long-term.
"He's a tough guy," Caldwell said. "He's tough, he's durable, he's typically been able to battle through a lot. If you play that position, literally, there's contact on every play and those guys get accustomed to being uncomfortable — until the point where it gets to be something that's out of his control."