Jim Harbaugh is not concerned about how his Michigan Wolverines (18) defense matches up with that of the Northwestern Wildcats (13).

"The two defenses won't go against each other in the game, they won't face other," he told reporters in his weekly press conference, according to ESPN.

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Michigan lost its season opener to Utah, a team that has remained unbeaten, climbed to fifth overall in the national poll and holds first place in the Pac-12 South. Since that loss, Michigan is 4-0 and has only allowed 14 points total during that stretch, which includes two consecutive shutouts.

At 5-0, Northwestern has a pair of shutouts as well and its average of seven points allowed per game is the best in the nation. With 7.6 points allowed per game, Michigan trails only Northwestern in that category.

Michigan will have to go without defensive end Mario Ojemudia, who is second on the team with six tackles for loss, recording at least one in each of the Wolverines' five games. Ojemudia is also a senior and his Achilles tendon injury ended his season.

In such a defensive struggle, field position will be important for both offenses, as will their pass rush and ability to disrupt plays in the backfield. For Northwestern, linebacker Anthony Walker will be important to that end.

"They react, as athletic and fast as anybody we've seen," Harbaugh said. "[Walker] is as good a player as we've faced. So all of those things, really good scheme, they play great team defense, leading the country in points allowed. I think that's the thing, mainly, is that this team reacts and flows to the ball as good as you're going to see in college football."

(Quotes, stats: ESPN)