GREEN BAY -- Brian Urlacher, a man who knows a thing or two about playing middle linebacker in the National Football League, has some friendly advice for the Packers as they try to replace injured Nick Barnett for Sunday's NFC North showdown with Urlacher's Chicago Bears.

"It's a tough position to kind of just throw somebody in there," Urlacher said during a conference call with Wisconsin reporters earlier this week.

Which is why the Packers are opting to move A.J. Hawk -- a starter at weak-side linebacker since being drafted No. 5 overall in 2006 -- to Barnett's spot in the middle rather than starting second-year man Desmond Bishop, Barnett's immediate backup who had two significant gaffes in last week's loss at Minnesota.

Of course, Urlacher is the same guy who had had no idea that Barnett had suffered a season-ending torn ACL in his right knee last Sunday at Minnesota -- until informed of it by a reporter (me) during Wednesday's speakerphone chat.

Given the bad news, Urlacher sounded genuinely disappointed. "Aw, that really stinks, man," he said. "He's a good player."

Then, unprompted, Urlacher offered his conjecture on the Packers' replacement plan, saying, "I'm sure they'll put Hawk ..." before stopping himself. "I mean, I don't know what they'll do."

That's what Packers coach Mike McCarthy was trying to tell everyone all week, too. While he wouldn't say definitively that he's going in that direction, Hawk has gotten the bulk of the reps in the middle, with No. 4 linebacker Brandon Chillar moving into the starting lineup at Hawk's spot. Bishop will back up at all three spots.

McCarthy said in his conference call with Chicago-area reporters that he would "rotate those three guys in," and he said during his news conference that "they're all going to be ready," although he acknowledged that by watching practice, it wasn't too hard to figure out what was going on.

"A.J. is getting a lot of work there," McCarthy said.

Barnett leads the Packers in tackles (68), while Hawk ranks third (55). Chillar spent several weeks earlier this season spelling Hawk in the nickel defense while Hawk recovered from a Sept. 28 groin injury.

Hawk never played in the middle in college at Ohio State and all 41 of his career regular-season NFL games have been played at will. He has rotated through the position during minicamp and training camp practices, however.

"Playing 'mike,' it's different," Hawk said after taking most of the practice snaps Wednesday in the middle. "When it comes down to it, it's all just still football. But you're just kind of seeing the game from a little bit different perspective, being in the middle of the field and running kind of inside-out to all the plays instead of chasing things from the backside, like you do at the 'will' postition a lot. I think it just takes a little bit of work to keep that view, that perspective of the game and feel how they're trying to attack you and do things.

"But like I said, when it comes down to it, football's a simple game. As linebackers, we try to tackle the guy with the ball. So that's my goal."

Hawk and Barnett had been the two defensive players with radio headsets in their helmets, so Hawk, who took over the defensive play-calling duties from Barnett after the injury, expects to do so again against the Bears.

"I called the defense in college; it's not too hard. I don't mind doing that," Hawk said. "I like being in there, in control of the huddle, and calling the defense, it keeps you in the game. It's not too big an adjustment for me."

However, when asked how losing their middle linebacker will affect them, Urlacher cited that change as the most significant or the other 10 players on defense.

"That's a tough thing because you've got to have a guy calling the defenses, and he's been that for six years now and they've probably grown accustomed to him calling the huddle," Urlacher said. "So it'll be a little different getting a new guy in there making the calls. But the next man up has to go; that's just the way it works."

Bishop, meanwhile, might have gotten the nod against the Bears if not for the two colossal mistakes he made against the Vikings after Barnett went down.

On his first play from scrimmage, Bishop overran running back Chester Taylor on a short checkdown pass to the left, allowing Taylor to sprint 47 yards for a touchdown. Then, on Adrian Peterson's go-ahead 29-yard touchdown run with 2:22 left in the game, Bishop evacuated his gap and went to where he thought Peterson would cut back, leaving Peterson an open lane toward the end zone.

"You can't think like that, but then again, it's in the back of my mind: Maybe if those two plays would've went the way I wanted to, then maybe they might've had a little more confidence in me," said Bishop, who also stripped Peterson on a crucial fourth-down play. "But you can't go back. I can only look forward."