The Bears reported Monday evening that Trubisky suffered a right shoulder injury in Sunday night's 25-20 victory over Minnesota, which gave Chicago a 1 1/2-game lead over the Vikings in the NFC North. Detroit (4-6) is last, one-half game behind Green Bay (4-5-1).
If Trubisky cannot go, Chase Daniel will get the start. Daniel, 32, is a career backup who began his career with New Orleans in 2010 and has completed 65.4 percent of his 78 passes with one touchdown and one interception.
"I know that Chase, this is one of the reasons why he's here, if we get in a situation like this where we have to make a decision one way or the other," Bears head coach Matt Nagy said. "This is why you have a guy like Chase.
"You feel very comfortable with him. Chase understands; he's the oldest guy on our team so he's got experience."
Nagy is still holding out hope Trubisky could start, and it will ultimately be a game-time decision.
"I'm saying cautiously optimistic, but I can't make any promises," Nagy said. "I hope he does. But it's a day-to-day thing for us."
Trubisky suffered the injury when he was hit late by Minnesota's Harrison Smith on his shoulder after giving himself up by sliding, and at the time had his right shoulder pressed against the ground under his body weight.
"It wasn't intentional," Nagy said. "Again, it is football. It is an illegal hit. You always want to look at things from both sides and you hope it's not malicious.
"But when it's a late hit, then it can be challenging for you. But it's, again, there are just so many variables that go into it. Mitch is a tough kid."
Daniel has more urgency than usual in a week when Chicago didn't really hold an official extensive practice. They had walkthroughs Monday and Tuesday.
"This week is a little bit different just because it's a short week, but I really haven't changed the way I prepare," Daniel said. "I prepare like a starter every week, so for me it's just another game."
Daniel hasn't had more than two throws in a season since he was with Kansas City in 2014. But he has extensive knowledge of the offensive system after being in it from 2013-15 while Nagy was the quarterbacks coach with Kansas City.
"Nags and I go way back, he was my position coach for three years in Kansas City, obviously, and we stayed close for my time away," Daniel said. "Yeah, we have a great relationship, so when it comes to that we trust each other pretty well. So we know what each other likes and I think we can just roll."
Trubisky was 23-of-30 passing for a career-high 355 yards with three touchdown passes in a 34-22 victory over Detroit on Nov. 11, ending a three-game losing streak versus the Lions. The clubs have split 16 Thanksgiving meetings with Detroit starting its tradition of playing on Thanksgiving in 1934, when Chicago prevailed 19-16.
The Lions snapped a three-game losing streak with a 20-19 victory over Carolina on Sunday -- surviving a two-point conversion attempt with 1:07 remaining -- and remain in must-win mode.
Detroit must move forward, though, without rookie running back Kerryon Johnson (team-high 641 rushing yards, three touchdowns). The second-round pick out of Auburn sprained his left knee against the Panthers and is week-to-week.
"I think we have good players, we have dynamic guys, guys that can make plays in different ways," Lions head coach Matt Patricia said. "And it's not cookie cutter. Football's not that way. When you have a different player that's in and in the same position, it doesn't mean that they can do the same thing. You have to be able to adjust for that and do a good job of handling that, whatever the situation is, whoever those guys are."
Detroit will try to patch together a running game with LeGarrette Blount, who is averaging a career-low 2.3 yards per carry and is on pace for his worst rushing season since 2012. Theo Riddick and Zach Zenner are other options.
The Lions have shored up their run defense, which ranked last in the NFL in the first half of the season, allowing an average of 142.5 yards. In games against the Bears and Panthers in the last two weeks, they've given up a total of 110 yards on the ground.