Back to the guessing game.

The Lions are still not letting on whether or not rookie Matthew Stafford — who won the starting quarterback job through a preseason competition that was kept as under wraps as possible by the Lions’ coaching staff — will continue in that starting role this weekend.

Stafford injured his knee in the fourth quarter of Sunday’s 48-24 loss to the Bears, and had tests done on Monday — which revealed no structural damage, and no need for surgery — but hasn’t practiced yet this week, as the Lions’ medical personnel try to get the swelling to subside.

If Stafford can’t go, veteran Daunte Culpepper will get the nod.

Either way, no one’s saying.

Head coach Jim Schwartz referred inquiring reporters to Thursday’s injury report, while Culpepper declined to talk at all.

“Daunte’s a pro. He has a lot of experience in the league. He looks about the same way he practiced in OTAs and training camp,” Schwartz said of the possibility of having to start Culpepper in Sunday’s game against the Steelers.

Stafford was in street clothes for practice both Wednesday and Thursday, and did not participate, but no one was ruling him out for Sunday.

“We’re not eliminating him,” offensive coordinator Scott Linehan said. “Rookie or 10-year vet, you’d like him to have all the reps. That’s part of the game. You have to deal with that, and figure out how you would manage it, if that’s the case, what you would do, game plan-wise, if he didn’t get the reps.”

For Stafford’s part, it would be a difficult spot to put a rookie in, facing a top-10 defense like the Steelers, one that limited San Diego to just 16 yards rushing in last week’s win, especially without having any live practice repetitions.

“The last two days — yesterday and today — I’ve just been trying to get as many mental reps as I can, staying extra, watching a bunch of film. These guys are a good defense. ... We’ll see. You try to do a bunch of work off the field, and get as ready as you can,” he said Thursday. “Football’s a physical game, no matter what level you’re playing it at. There’s always that chance (of injury), and you’ve just got to deal with it, as best you can.”