Success has been hard to come by for the Bears when LB Brian Urlacher is not starting. (US Presswire)

The Bears' defense hasn't held up well in the past without LB Brian Urlacher, but they're hoping circumstances are different this time.

A centerpiece of GM Phil Emery's plan to improve the team was adding depth, and LB Geno Hayes was part of this. He'll move into the lineup at strong side LB, and strong side LB Nick Roach will play middle against Minnesota. 

Hayes (220 pounds) is a bit undersized for strong side in the Bears scheme. He started his final three seasons in Tampa before coming to Chicago. Hayes played in a similar system with the Bucs, then got extensive playing time in training camp this year when Urlacher was recovering from arthroscopic knee surgery.

"This is not my first time around, this is not my first rodeo," Hayes said. "It was great getting the good experience in preseason and get accustomed to the defense and accustomed to the guys I was out there playing ball with day in and day out. So, it was great."

Hayes had 42 starts for the Bucs in the last three of his four seasons and had four interceptions and forced four fumbles.

What the Bears are lacking with Hayes and Roach instead of Urlacher and Roach is beyond measuring. Although Urlacher's speed has obviously decreased this season, he still runs the defense.

"We're missing a great player," coach Lovie Smith said. "You just have to go with Plan B. Plan B for us is pretty good if you do lose a player like that."

Urlacher has missed 22 games with the Bears while they've played in Smith's scheme, and they have fared poorly without him.

The Bears are 7-15 in starts without Urlacher. The defense allows just over six points per game more when they don't have him. The third-down defense is considerably less effective, allowing 39 percent conversions without him and 33 percent with him.  Yardage-wise it's about 31.5 more yards allowed per game.

"You can’t replace that," Hayes said. "Urlacher is one of a kind. You can try to play like that … everybody wants to treat certain guys and say, ‘He’s like this,’ or ‘He’s that,’ but you can’t make too many guys like Brian Urlacher. 

"He is a special guy."

The Bears hope the difference this time is Roach has not only played in the middle in preseason and in three games in 2009 but that he is a more seasoned player who can handle leadership, play calls and presnap changes that Urlacher would have been providing. Roach had only about a full season's worth of experience when he moved from strong side to middle in 2009. The Bears went 1-2 in those games, allowing 90 points. Those three games included a 45-10 loss at Cincinnati. After that game, MLB backup Hunter Hillenmeyer was healthy and came back, so Roach moved to strong side.

Roach is laid back and quiet, at least when talking with media.

"But when he is on the field he is very vocal," Hayes said. "Also, it is good because he plays Sam (linebacker), the same position I am playing right now so if I have any questions on the field I can ask him and he will be inciteful. So it will be great."

The Bears' defense is coming off its worst game of the year yardage-wise, but held Vikings RB Adrian Peterson to 25 first-half rushing yards while taking a 25-3 halftime lead two weeks ago. Accomplishing something similar will be difficult without Urlacher.

For Roach and Hayes, making a statement could go a long way toward their future. Hayes is working on a one-year deal. Roach's contract expires after this season.

"I try not to think about those things," Hayes said. "I just want to go out there and play ball. Contract, that stuff is for after the season." 

Follow Bears reporter Gene Chamberlain on Twitter @CBSSportsNFLCHI.