The 49ers’ monthlong sack slump could be nearing its end.

And that’s because the Seahawks are up next.

The attention paid to Seattle’s signing of Marshawn Lynch to bolster their depleted backfield has helped obscure its larger offensive issue: The Seahawks’ injury-thinned offensive line, which has allowed the seventh-most sacks in the NFL, was particularly putrid in pass protection in a 27-13 loss to the Cardinals on Sunday.

In fact, it won’t matter if Lynch, 33, has a turn-back-the-clock performance if the Seattle line can’t do a better job of keeping its most important player, quarterback Russell Wilson, upright.

Asked what gave him optimism that Seattle’s front five would be improved when it faces the 49ers on Sunday night, Seattle head coach Pete Carroll adopted a sarcastic woe-is-us tone.

“Well, I don’t know,” Carroll said on a conference call with the Bay Area media Tuesday. “We’re just going to try to scrap it together the best we can. I don’t know. We’ve just got to figure it out. I hope we can make it.”

Carroll was later asked a similar question by Seattle reporters.

“We’re going to go about it,” Carroll said. “That’s under way.”

Carroll obviously didn’t have strong answers. And it’s possible his offensive line won’t have any against the 49ers, who rank fifth in the NFL in sacks but have just three in their past four games. The 49ers had five sacks in a 27-24 overtime loss to the Seahawks on Nov. 11.

Against Arizona, the Seahawks allowed four of their five sacks to Pro Bowl pass rusher Chandler Jones, who took full advantage of the absence of Pro Bowl left tackle Duane Brown (knee). Brown won’t play against the 49ers, meaning backup left tackle Jamarco Jones, a 2018 fifth-round pick with three career starts, might try to rebound after he was routinely beaten by Jones.

Given Jones’ struggles against Arizona, the Seahawks could replace him with George Fant, who has 23 career starts.

“It was hard,” Carroll said when asked about Jones’ performance. “He went against a great guy and it worked him the whole day. He did a lot of things that were really good. The sacks (Chandler Jones) had weren’t all on him. And it didn’t all happen because of his protection. He was tested. That was a real test. Chandler’s an amazing player.”

The 49ers figure to test Jones or Fant with edge rusher Nick Bosa (nine sacks), the front-runner to be named the NFL’s Rookie Defensive Player of the Year.

And the rest of Seattle’s front will have to contend with defensive linemen Arik Armstead (10 sacks) and DeForest Buckner (6.5). Beyond Brown’s absence, the Seahawks also are without starting center Justin Britt, who is on injured reserve with a knee injury.

Sunday’s game Who: 49ers (12-3) at Seattle (11-4) When: 5:20 p.m. TV: Channel: 11Channel: 3Channel: 8 Radio: 104.5, 680, 107.7

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The 49ers are dealing with defensive-line injuries. Dee Ford (hamstring), who won’t play Sunday, has played four snaps in the past four games; in two of them, the 49ers haven’t managed a sack.

Still, the Seahawks’ most recent performance suggests the 49ers’ front could, again, flourish in a game that will determine the winner of the NFC West.

Against Arizona, Wilson completed just four passes to wide receivers, and Carroll indicated that was because he rarely had time to look downfield.

Wilson expressed confidence after the game that the Seahawks could cure what ailed them. Like Carroll, though, he was short on specifics.

“I don’t think there’s anybody better than us,” Wilson said, “to try to figure out how to answer.”

Suspect arrested: Nashville Police said Wednesday it had arrested the man accused of the fatal stabbing of Clayton Beathard, 22, the younger brother of 49ers quarterback C.J. Beathard, and another man outside a Nashville bar early Saturday morning.

Michael D. Mosely was located in a vacant home outside Nashville. He was booked on two counts of criminal homicide and one count of attempted criminal homicide.

Eric Branch covers the 49ers for The San Francisco Chronicle. Email: ebranch@sfchronicle.com Twitter: @Eric_Branch