By Chris Emma—

(CBS) So often regarded as inconsequential, this preseason means a great deal for the rebuilding Bears.

Coach John Fox has said that this roster is by far the best he has seen in three years in Chicago, citing the quality competition across the depth chart.

Competition certainly seems clear for a roster loaded with position battles, but it’s just as important to identify depth at every position – especially for a team that hasn’t been able to play next-man-up football the last two years.

The Bears will get an important evaluation of their roster and its depth when they host the Broncos on Thursday night at Soldier Field in their preseason opener. There’s plenty for Fox to see as he assesses where this team stands.

Here’s what to watch for:

Arms race

The Bears face the challenge of developing Mike Glennon as their 2017 starting quarterback, Mark Sanchez as their backup and rookie Mitchell Trubisky as their future. It’s one of the most unique quarterback situations in all of football and one that will be under the microscope come Thursday night.

Each of the Bears’ three quarterbacks in uniform Thursday need reps for his own role. It’s likely that Glennon plays two or three series, then Sanchez finishes the first half and Trubisky takes the second half mostly to himself.

Fox and the coaching staff must get a good look at each of their three arms.

Can Shaheen shine?

The next big step for rookie tight end Adam Shaheen, a second-round pick who went to Division-II Ashland, comes on Thursday night when he faces another team’s defense in a game situation. Can he look the part?

Shaheen has managed well during the early part of training camp, showing he can use that size and athleticism to create space and make plays. The Bears seem to be gaining more confidence in Shaheen, and he could get some looks with the first-team offense on Thursday.

O-line shuffle

Veteran guard Kyle Long isn’t likely to play Thursday as the Bears ease him back from an offseason ankle rehab. He took just 10 reps in live action Tuesday morning, which marked an increase in reps.

As the Bears slowly return Long – with Fox stating that the three-time Pro Bowl guard is “on target” to play in Week 1 – they’ve moved Cody Whitehair to left guard and slid Hroniss Grasu in at center. That will be something to watch during Thursday’s contest and a formula that may need to be used if Long isn’t ready for the regular-season opener on Sept. 10.

High five

General manager Ryan Pace has done good work rebuilding the Bears’ front seven, which has been almost entirely overhauled from the previous regime. But the one missing piece to Pace’s personnel remains at the five-technique opposite Akiem Hicks.

The Bears are giving a good look at Jonathan Bullard, the 2016 third-round pick who’s finally showing he’s better prepared for the rigors of the NFL, as defensive coordinator Vic Fangio said. The team will also give a look to veterans Jaye Howard and Mitch Unrein.

Early on, this seems like Bullard’s job to lose.

Safety dance

At safety, it’s a revolving door next to Quintin Demps, with the Bears still identifying their best fit in the secondary. We may have a better idea of their plans come Thursday night.

Adrian Amos has been a two-year starter at safety for the Bears, but he still has zero interceptions in those 31 games. Have they seen enough of Amos? Rookie Eddie Jackson has been impressive in coverage during the early part of training camp and could win over that job.

Deon Bush, Deiondre’ Hall and Harold Jones-Quartey will also get their cracks at the starting spot. However, this one may come down to Amos and Jackson.

Chris Emma covers the Bears, Chicago’s sports scene and more for Follow him on Twitter @CEmma670 and like his Facebook page.

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