It’s been awhile since the Gophers’ primary concern was their defense, but that’s the situation heading into an important home game Saturday against Illinois.

The offense has overcome injuries to three starting linemen to find a relatively good groove, especially for quarterback Mitch Leidner. But a defense hit even harder by injuries just surrendered 506 yards to Iowa, the most the Gophers have allowed since their 2011 loss to Nebraska.

Next, they’ll face an Illinois squad that racked up 596 yards at Purdue two weeks ago before getting held to 261 yards and three points last week against Ohio State.

It should be an interesting chess match between Gophers coach Tracy Claeys, the team’s longtime defensive coordinator, and Illinois interim coach Bill Cubit, a noted offensive strategist.

“He’s got a great mind for taking the traditional personnel [groupings] and putting them in nontraditional formations,” Claeys said. “You can draw all night long, and he’s going to come up with a couple things that you’re not going to come up with. So the kids really have to communicate and make those adjustments on the field.”

The Gophers were 6-1 and 5 ½-point favorites heading to Illinois last October. With starting quarterback Wes Lunt injured, Cubit came up with some wrinkles for backup Reilly O’Toole, and the Illini jumped to a 14-0 first-quarter lead in an eventual 28-24 upset.

That Minnesota defense was a lot healthier than the one Claeys and fill-in defensive coordinator Jay Sawvel are working with this week. It sounds as if Gophers again will be without two starting defensive tackles (Steven Richardson and Scott Ekpe), two safeties (Damarius Travis and Ace Rogers) and two cornerbacks (Jalen Myrick and Craig James).

With a similar injury situation two weeks ago, the Gophers held Ohio State to 28 points in Columbus, with 21 coming against the defense and seven coming on an interception return by Buckeyes safety Vonn Bell.

Iowa did a better job exploiting the Gophers’ weaknesses, controlling the line of scrimmage, especially in the middle, where Minnesota misses Richardson and Ekpe. Sophomore Andrew Stelter has rotated with those two all season, but the injuries have thrust Yoshoub Timms, Gaelin Elmore and Robert Ndondo-Lay into defensive tackle duty.

“Andrew’s done a great job for us up front,” Claeys said. “Gaelin Elmore has played well and Shooby [Timms]. But those kids are still not — they don’t have the same strength that our first two guys do.”

The Gophers have stayed relatively healthy at linebacker, with Jack Lynn (team-high 9 ½ tackles for a loss), Cody Poock (73 tackles) and De’Vondre Campbell (66 tackles) consistently making plays. The one exception was the 48-25 loss to Nebraska. Poock missed that game because of an injury, and Campbell was limited, one night after the birth of his first child.

Against Illinois, the Gophers’ biggest concern could be the secondary. The Gophers have decorated senior cornerbacks Eric Murray and Briean Boddy-Calhoun, but without Myrick and James, the two other cornerback options are true freshmen KiAnte Hardin and Antonio Shenault.

Senior safety Antonio Johnson leads the team with 79 tackles, but without Travis, the Gophers have been asking a lot of sophomore walk-on Adekunle Ayinde.

Cubit has been taking notes. Lunt is back healthy, and Illinois likes to run four-receiver sets.

“Hopefully we’ll be able to get some pressure with the front four [on the defensive line] because they like to play four wides a lot,” Claeys said. “Where we’re at in the secondary, injury wise, that’ll be a challenge.”

Etc.

• Claeys said running back Rodney Smith (ankle) is probable for the Illinois game.

• Redshirt freshman Jerry Gibson has switched from tight end to defensive end, Claeys confirmed.