The Chicago Bears destroyed the Buffalo Bills 40-7 the last time these teams faced off at Soldier Field, but this season features two vastly different clubs when they meet Sunday in the regular-season opener.

Interestingly, the Bills struggled throughout the preseason due to shoddy play at quarterback. Chicago's revamped defense didn't inspire much confidence throughout the preseason, either. So something has to give here.

ESPN.com Bears reporter Michael C. Wright and Bills reporter Mike Rodak delve deeper into this matchup:

Wright: It looks like the Bills have a few injuries that could affect this game. Can you give us a rundown of the situation?

Rodak: The main injury is to Sammy Watkins. The success of the Bills this season could hinge on Watkins -- after all, the team spent two first-round draft picks on him -- so naturally there is a lot of attention on his ribs. He first injured them in the third preseason game. After sitting out the fourth game, he returned for the fifth game but quickly re-injured the area on a similar hit. As far as we know, they're not broken, but coach Doug Marrone has stressed that rib injuries can change over time; one day they're feeling good, the next they're not. I'd lean toward Watkins playing Sunday but he admitted Monday that he may need to take some plays off as a pain-tolerance measure. Otherwise, the Bills are fairly healthy. Tight end Lee Smith (toe) is the only other injury at this point. He's the Bills' blocking tight end in their running game.

With Jay Cutler, Alshon Jeffery, and Brandon Marshall, you could argue the Bears' passing game is underrated. How would you rank their aerial attack among other NFL teams and how has the offense evolved with the change from Lovie Smith to Marc Trestman?

Wright: Statistically, the Bears finished 2013 ranked fifth in the NFL in passing offense and I'd say they're definitely still a top-5 team in that area, given the experience gained under Trestman in his first year. Marshall and Jeffery finished with a combined 2,716 yards receiving, which ranked as second most among any NFL duo in 2013. Marshall and Jeffery want to be No. 1 in 2014, and there's a good chance of that happening. If you go back to last year, Marshall underwent arthroscopic hip surgery in the offseason, and instead of training in the lead-up to camp, he was rehabbing. That led to missed time at camp and Marshall getting off to a slow start. He didn't hit his stride until about halfway through the season. I think that's why Marshall often says that 2014 will be his Michael Jackson "Thriller" year. So I'm expecting another big season from Marshall.

In terms of how the offense has evolved, it's definitely been a complete 180 from what this team did with Smith in charge. Because of Smith's defensive background, the Bears leaned heavily to that side of the ball during his tenure. It's been the opposite with Trestman. What's more, Trestman and offensive coordinator Aaron Kromer have installed a system in Chicago that Cutler believes in very strongly. That's important because in the past, Cutler didn't believe in what the team was doing offensively. Now that Cutler has completely bought in, you're starting to see him live up to all the potential. You should see another jump in Cutler's game this season now that he's totally comfortable in Trestman's system.

Buffalo's offense struggled in the preseason. Why, and is it cause for concern heading into this game in Chicago?

Rodak: Most of the blame for the struggles has been pinned on the quarterbacks, and rightfully so. EJ Manuel played in all five preseason games and didn't prove that he has progressed from where he ended last season. Manuel and the first-team offense didn't score a touchdown until their 19th drive, early in the third quarter of the fourth preseason game when the Tampa Bay Buccaneers pulled their starting defense. Accuracy can be a problem for Manuel at times, but he completed at least 63 percent of his passes in the second, third, and fourth preseason games, so that's not the issue. Nor are interceptions -- he had only two of them in the preseason. Instead, I point to Manuel's reluctance to push the ball downfield. His yards-per-attempt numbers are typically low and many of his completions come on dump-offs and check-downs. If the Bears take away the intermediate and deep part of the field, Manuel won't challenge them. He'll target his tight ends and running backs, which is what opposing defenses will want.

There are some familiar Bears -- Lance Briggs, Charles Tillman and Tim Jennings -- but also several newcomers on Mel Tucker's defense. How have the additions of Jared Allen and Lamarr Houston, as well as the turnover at safety, affected the unit?

Wright: I wish I could tell you, but the truth is we don’t really know just yet as the defense operated with vanilla game plans throughout the preseason, and we never saw a full starting lineup on the field. Allen played in only one preseason game, and free safety Chris Conte didn’t even make his debut until preseason game No. 3. So I don’t think we know the true potential of this unit, or whether it will be able to turn things around after performing historically bad in 2013. What I have noticed is the Bears are scrappier up front with the additions of Allen, Houston and Willie Young to go with draft picks Ego Ferguson and Will Sutton. We saw lots of fights in the offseason and in training camp. Even first-round pick Kyle Fuller shows that he’s got some toughness in him. At the start of the offseason, the Bears said they wanted to make the defense a much tougher unit than it was in 2013, and from what I’ve seen so far, they’ve accomplished that. But going into the opener, we still don’t even know who the starting safeties are, even though sources have told me Conte -- if he’s cleared to play after suffering a concussion in the preseason -- and Ryan Mundy will be the starters on the back end.

Eighteen out of the 64 voters picked Watkins as NFL Offensive Rookie of the Year when we did our predictions. We didn’t see much production from him in the preseason. Is he the real deal?

Rodak: I think so. His lack of production traces back to his lack of playing time. He played only a few drives in the Hall of Fame game and second preseason game, and then was injured in the third game. Watkins has all the ability in the world. He'll make defenders miss after the catch, he'll beat them deep, and he'll snag errant passes over the middle. There are two questions with him right now: (1) Can he stay healthy? We've now seen two rib injuries in three weeks, with the second "deeper" than the first, according to Watkins. If he suffers a third, will it be worse? He took hard hits from Ryan Shazier and Ashlee Palmer that led to the injuries, but they weren't bone-crushing blows. They're the sort of hits he'll need to withstand in the NFL. (2) Does he have the right quarterback? Put Watkins on most other NFL teams, especially one with a top-flight quarterback, and he'd be the favorite for NFL Offensive Rookie of the Year. Having Manuel throwing passes isn't an ideal situation for the fourth overall pick.

How are fans in Chicago approaching this opener? The Bills and Bears have met only twice in the past decade, Chicago winning both times. Did fans breathe a sigh of relief when they saw Buffalo first on the schedule?

Wright: That’s funny, but I think Bears fans know from recent experience to not ever underestimate an opponent. The fan base knows the Bills are going to be a better team than we’ve seen in the past. I’d say the fans are definitely optimistic about the 2014 season, and in the five years I’ve covered this team, this is about the most excited I’ve seen the fan base about this team. Expectations are definitely soaring, but the optimism is tempered somewhat by the unknown regarding Chicago’s defense.