I didn’t think it was possible — and maybe it’s just because of the prolific offense the Bears are facing this week in the season opener — but I actually have more concern about the Bears’ defense — which has been a staple of the team’s success for years — than I do about the rebuilt offense.

In years past, ever the optimist, I knew that if the Bears struggled offensively, they at least could count on their defense to keep the game close and, sometimes, even win ballgames.

This year, after what we’ve seen in 2007 and through four meaningless practice games, I have serious reservations about this unit.

Sure, it’s a group that boasts a cast of Pro Bowlers like Tommie Harris, Brian Urlacher, Lance Briggs, Nathan Vasher, Mike Brown, Alex Brown, Adewale Ogunleye, and a Pro Bowl caliber corner in Charles Tillman. But the way these guys have overrun the ball carriers and whiffed — sometimes badly — on tackles is disconcerting.

The offense, meanwhile, won’t be confused for the 2006 squad which had three 40-point games and four 30-point games. But an argument can be made that they upgraded at both running back and quarterback, maintained — and even improved with the addition of rookie Kellen Davis — their stability at tight end, and even though they lost their starting wide receivers, the depth they currently have at the position allows them to do many things. The only area of concern I have for this unit is a pretty big area — offensive line. Because, if this group of “big uglies” up front can’t block, that prohibits the offense from both running the ball and passing it.

Maybe it’s just my nervous nature. I used to get jitters before every football game I played in and I still get a smidge of anxiety before laid-back men’s softball games.

Maybe it’s because for so long, we as Bears fans have had such low expectations for the offense that if they do bad, it’s to be expected. But if the defense does bad, we’re all in for a long year.

But I keep having visions in my head of Bears defenders slipping and sliding on a dry field as running backs glide untouched downfield. I keep seeing receivers finding the soft spots down the sideline in the Bears’ zone defense. I see a bend-but-don’t-break defense pushing itself to the breaking point.

As was the case in my playing days, I’m sure all this nervous, pent-up energy will be released come kickoff, but I’ll be closely watching this defense as I know they have a lot to prove not only to me, not only to the rest of Bear Nation, but the entire league as well.