The story of Northwestern’s 4-0 start has been more about its defense than its offense.

The No. 16 Wildcats rank 99th in the nation in scoring offense at 25 points per game, with victories over Stanford (16-6) and Duke (19-10), two teams with strong defenses.

“The biggest challenge with Northwestern is they’re a very well-oiled machine on offense,” Gophers senior cornerback Eric Murray said. “They have a lot of concepts they run, and if you don’t have those concepts, big things can happen to you on defense.”

The Gophers (3-1) will need to overcome their injuries and be ready Saturday when they visit Evanston, Ill., to face Northwestern in their Big Ten opener.

Defensive coordinator Tracy Claeys explained the Wildcats run a no-huddle offense with four or five different personnel groupings. Northwestern quickly alternates between using zero, one or two running backs, and one or two tight ends.

Of the Gophers’ previous opponents this season, only Colorado State used that many combinations, and Northwestern does it at a faster tempo.

So Gophers coaches and players will need to react with quick decision-making and communication, which could prove difficult because of the injuries. When they were at full strength, with four seniors in their secondary, this wasn’t the same concern.

At safety, Damarius Travis remains out because of a hamstring injury, but Gophers coach Jerry Kill said Thursday that Antonio Johnson could return. Johnson was going through Phase 2 of his concussion protocol but was not listed on the team’s injury report.

Even if he returns, the Gophers will continue to rely on sophomores Adekunle Ayinde and Duke McGhee and junior Ace Rogers at safety.

At cornerback, the Gophers will have Murray and junior Jalen Myrick, but senior Briean Boddy-Calhoun is “real questionable” because of a right knee injury, Kill said. KiAnte Hardin (ankle) returned to practice Wednesday, which could help the team’s depth. Antonio Shenault, another true freshman cornerback, like Hardin, had five tackles last week.

“I think it’s a great thing moving forward for the program to have such young people in those roles,” Murray said. “Because not so long ago, that was me, that was Briean and that was Damarius and Antonio.”

Etc.

• The Gophers listed Demry Croft as their backup quarterback for the first time on this week’s two-deep roster. Chris Streveler had been listed there, but Croft had been getting all the second-team reps in warmups.

• Kill said the Gophers will have linebacker Cody Poock back from his rib injury, so that should help, too. Poock leads the team with 28 tackles.

• The Gophers will have their same starting offensive line for the third consecutive week — left tackle Jonah Pirsig, left guard Joe Bjorklund, center Brian Bobek, right guard Connor Mayes and right tackle Josh Campion.

• Claeys said Northwestern quarterback Clayton Thorson, a redshirt freshman, is “kind of a lot like Mitch [Leidner]. … When they needed to make plays, they’ve made [them] in order to win the ballgame.”

• Wildcats sophomore running back Justin Jackson ranks second in the Big Ten with 516 yards.

“He’s got great vision, great speed,” Kill said. “If you don’t get him wrapped up, he’s going to bounce off of you.”