By Dan Durkin-

(CBS) Last season, the Bears were one of three teams to start the same five offensive linemen for all 16 games. A quarter of the way through this season, the Bears haven’t been nearly as fortunate.

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Just when it appears that Chicago may be closer to getting back center Roberto Garza and left guard Matt Slauson, who haven’t played since the season opener, a new injury has cropped up.

During Wednesday’s practice, left tackle Jermon Bushrod suffered a knee injury, and he didn’t participate in Thursday’s practice. Bears coach Marc Trestman said the injury happened accidentally, but the team remains optimistic it won’t last too long, and he added it’s a day-to-day evaluation.

“Certainly, it’s an unfortunate incident,” Trestman said. “Certainly, you don’t want to get anybody hurt, then it happens accidentally at practice. That’s what makes all this uncomfortable, but we’ve got to move forward, and we will.”

Michael Ola practiced at left tackle in Bushrod’s place, but offensive coordinator Aaron Kromer is continuing to work a variety of combinations along the line.

“We moved a bunch of guys there (left tackle) today,” Kromer said. “We’re just going to have to decide as we go. What we did today was rotate guys in and out and rotated different guys playing the ‘big’ (extra lineman) tight end. We rotated guards today, we rotated centers today. So, Slauson got some reps, Garza got some reps, so everybody was back getting reps.”

Defensive tackle Jeremiah Ratliff also didn’t participate in Thursday’s practice, as he hasn’t passed the concussion protocol.

Linebacker Shea McClellin (hand) and safety Ahmad Dixon (hamstring) sat out, too. McClellin has already been ruled out for Sunday’s game.

Here’s the injury report from Thursday.

Limited participation
— DE Jared Allen (illness)
— CB Sherrick McManis (quad)
— G Matt Slauson (ankle)
— C Roberto Garza (ankle)

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Full participation
— WR Brandon Marshall (ankle)
— S Chris Conte (shoulder)
— LB Lance Briggs (knee)
— LB D.J. Williams (neck)

Shotgun in short yardage

At the beginning of the second quarter against the Packers, the Bears ran back-to-back plays from the shotgun from the 1-yard line — a pass and a run — and were unable to score. Instead, they settled for a 23-yard field goal in what amounted to a missed opportunity for the offense.

When questioned about the decision, Kromer pointed to last season’s success in similar situations.

“If you recall last year, we were very effective in the shotgun both running it and passing it in the red zone, inside the 1-yard line,” Kromer said. “We ran some up the middle plays that scored, Matt Forte walked in cleanly a couple times. Those were the plays that were called, and they just didn’t work this time. We didn’t block them as well. We didn’t throw and catch them as well.”

Finishing in the red zone

The Bears piled up 496 yards against the Packers but were inefficient in the red zone, scoring touchdowns on two of their four trips.

Considering how the roster is composed and it being year two of the Trestman offense, the expectations were the offense would carry the load. Yet through a quarter of the season, the Bears are averaging only 21 points per game, which is below the NFL average (23).

Oddly enough, in the four games the Bears have played this season, the team that has outgained the other in yardage has lost each time. The Bears must finish drives with touchdowns, which is a focus for Kromer.

“I don’t think we can expect more than 500 yards of offense,” Kromer said. “But as far as points, yeah, we have to finish drives better. They did a good job on defense and we didn’t do a good job on offense and we’re used to doing that. We have been very productive inside the 10 and inside the 20-yard line and in that particular game we were not. We expect wholeheartedly to score when we get that close.”

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Dan Durkin covers the Bears for CBSChicago.com and is a frequent contributor to 670 The Score. Follow him on Twitter at @djdurkin.