CHICAGO -- A preseason opener shouldn’t cause panic. But what’s clear is that two of the main concerns for the Chicago Bears coming into 2012 -- the new offense, and the offensive line -- remain issues for this team coming off a 31-3 throttling Thursday night courtesy of the Denver Broncos.

The Bears held out quarterback Jay Cutler and running back Matt Forte on offense, while defensive stalwarts Brian Urlacher and Julius Peppers were also out of action.

The absence of Cutler and Forte on offense shouldn’t have made much of a difference, considering the club acquired their backups -- Jason Campbell and Michael Bush -- with the thought of maintaining a high level of performance in the event the starters missed time.

That didn’t happen as Campbell, and Josh McCown suffered a combined three sacks while Bush and Kahlil Bell came together for 13 yards on nine attempts.

“Set the bar is what we did in the first half,” Bears coach Lovie Smith said. “(I’m) not pleased in all three phases.”

Smith shouldn’t have been. But it’s important to remember it was just Game 1 of the preseason.

What it means: The Bears probably aren’t where they expected to be in terms of the development of the offensive line. So they’ll take full advantage of the remaining time at camp to work through its issues on the offensive line. In all, the line gave up four sacks, while struggling to open up holes in the running game.

So it wouldn’t come as a surprise if offensive coordinator Mike Tice tinkered some with the lineup in the team’s preparation for the Aug. 18 game against the Washington Redskins.

Unexpected starters: Cutler warmed up in full uniform several minutes before kickoff, but didn’t come out with the first-team offense. Instead, the Bears opted for second-team quarterback Campbell, who completed 4 of 5 for 13 yards and a passer rating of 79.9 while taking a sack.

“We were going up against a tremendous defense. We’re not trying to do anything to really show our hand or show what we have right now,” Campbell said. “We’ve had a great training camp, and we wanted to get out here and get our offense going, but they did a good job of covering us up early on. We’ve got to take what the defense gives us and keep competing. This is our first day out here. It’s my first time playing in 10 months, so we just have to get back going again.”

The defense played without Peppers and Urlacher, who was recently excused from the team to attend to a personal matter. Corey Wootton started in Peppers’ place, while Nick Roach filled in at middle linebacker with Geno Hayes sliding over to Roach’s spot at strong side linebacker.

At running back, Bush made his Chicago Bears debut with the starters because Forte was held out. Forte suffered a minor hand injury during a training camp workout. So it’s likely the team held him out as a precautionary measure.

Bush finished with 2 yards on three attempts.

Unhappy return: Quarterback Caleb Hanie spent the first four years of his career with the Bears before signing in March with the Broncos. It’s obvious that Bears fans haven’t gotten over the role Hanie played in the team’s 2011 collapse, judging by the reception the Soldier Field crowd gave upon the announcement the quarterback would be entering the game.

Hanie trotted onto the field to loud booing from the crowd, which became even louder when he threw his first incomplete pass.

The Bears started the 2011 season 7-3 before Cutler suffered a season-ending thumb injury that thrust Hanie into the starting lineup. With Hanie at the helm, the Bears lost four in a row to fall out of contention for a postseason berth, and he finished the season completing just 50 percent of his passes for a rating of 41.8 with three touchdowns and nine interceptions.

Hanie hit on 7 of 14 in the first half for 79 yards, including a 20-yard completion to Cornelius Ingram.

Former Chicago Bears fifth-round pick Josh Moore also made his debut with the Broncos. Drafted in 2010, Moore played in three games as a rookie and spent some of 2011 on the Bears’ practice squad.

Up and down debut: Rookie defensive end Shea McClellin sacked Hanie for a 10-yard loss with 27 seconds left in the first quarter. But the rest of McClellin’s debut garnered mixed reviews. While McClellin consistently displayed the speed the Bears raved about upon drafting him, the rookie struggled when engaging blockers, a problem he’s faced throughout training camp. On some occasions, opposing tight ends easily handled McClellin, which is somewhat concerning considering he’ll often be matched up against offensive tackles.

McClellin also received a 15-yard personal foul penalty at the end of the first half for a blow to the head on Hanie.

The one positive to take from this is the fact the regular-season opener isn’t until Sept. 9. McClellin has shown gradual improvement throughout training camp, but needs to refine his technique even more to be a key contributor in the regular season.

“It’s always good in your first (game) to get a sack to start off your career,” Smith said. “That’s good.”

What’s next: The Bears resume training camp workouts at Olivet Nazarene University on Saturday in preparation for their Aug. 18 matchup at Soldier Field against the Redskins.