ALLEN PARK -- How are the Detroit Lions going to replace Kerryon Johnson?

No bigger question faces this team as they try to figure out how to crack a Bears defense that ranks fourth in points allowed, third in yards allowed and first in -- you guessed it! -- yards allowed on the ground.

Rushing yards per game? Rushing yards per carry? You name it, this defense leads it. Just ask the Vikings, whose running backs were held to 17 yards on 13 carries Sunday night. Heck, ask the Lions. When they played Chicago nine days ago, they needed almost the entire first half to get on the scoreboard -- by which point, they trailed 26-0.

Johnson did have a bit of luck in that game, scoring once on the ground and again through the air. But he finished with just 51 yards on 14 carries, an average of 3.4 yards a pop -- 2.0 yards off his season average.

Now the Lions have to turn around and see that defense again on the short week, and in all likelihood, do so without their rookie sensation. Johnson, who ranks sixth in the league in yards per carry, sprained his knee in the third quarter of Sunday's win against Carolina. He is week to week, according to ESPN, which means he's not expected to play on Thanksgiving against the Bears.

"We'll take it day-by-day," coach Matt Patricia said. "We'll see how it goes. We just have to stay even-keel with all of it and make sure we prepare like we're just pushing forward."

So back to the question at hand: How are the Lions going to replace Kerryon Johnson?

Free agency is likely out of the equation because the short-turnaround leaves so little time for learning a game plan, let alone a playbook. That means in-house options like LeGarrette Blount, Theo Riddick and Zach Zenner could be candidates for larger roles against the Bears.

Blount has been the No. 2 rusher all season, but his struggles are starting to pile up. He's too big to run away from people, and isn't breaking tackles right now either. He ran seven times for 1 yard against Carolina, and is coming off a month where he rushed 24 times for 16 yards.

Riddick has played a lot this year, but been used sparingly as a ball-carrier. He's rushed nine times for 30 yards, and averages just 3.4 yards per carry for his career.

An intriguing option at the back end of the rotation is Zenner. He just re-signed with the club two weeks ago, but has been playing in this offense since 2015. He's averaged a pedestrian 3.6 yards on 120 career carries, but has had some success as an injury replacement.

With Ameer Abdullah and Riddick both banged up late in 2016, Zenner earned his first career start in the backfield in Dallas on Monday Night Football. And a back who was averaging 3.5 yards per carry for his career exploded for 64 yards on 10 carries in the first half alone.

Detroit had to go away from him in the second half, as the club fell behind by double digits, but he still scored twice and finished with a career-high 67 yards. And then he topped it again the following week, rushing 20 times for 69 yards and one touchdown with the division hanging in the balance against Green Bay.

The Lions lost the division that day, but Zenner played well. Is he ready to do it again?

"Absolutely," Zenner said. "I mean, first though, no matter what it means for me, it's always disappointing to see a teammate get injured, no matter what the situation is. And it's no different for this one. Kerryon is a good teammate, good person, good friend, so it's certainly tough to see him have an injury. I don't know what the situation is, I don't know when he'll be back. But if not, I'll do whatever I can."

What has Zenner learned about what it takes to succeed in these kinds of situations?

"Just not try to do too much," he said. "Stay within your own strengths. Try to help out the team as much as you can in that area. Try not to go outside of yourself and be something you're not."

What Zenner is, is a no-nonsense runner. He doesn't have Blount's strength or Johnson's athleticism. But he knows the playbook, and he's sure handed. He can take the football, and when he sees a crack, he'll try to hit it.

He won't hit a home run -- his career-long run is 20 yards -- but he has enough experience to not strike out either. He's done this before. And he's in the best shape of his career, trimming his body fat from 12.6 percent to 8.0, and packing on 14 pounds of muscle while he was away from the team at the start of the season.

Now it seems he just might get a shot to show the Lions what he's got.