The San Francisco 49ers will be without one of their critical pieces on defense against the Seattle Seahawks, with defensive tackle Arik Armstead unavailable because of foot and knee injuries.

Armstead is enjoying his finest season since the 49ers’ Super Bowl campaign of 2019. He is seventh in Pro Football Focus pass rush grade among interior defensive linemen and has racked up 42 pressures.

His proficiency for creating consistent interior pressure alongside defensive tackle running mate Javon Hargrave has been crucial to the 49ers’ success on defense since the bye week.

But with Armstead out of the lineup this week, another former first-round pick, Javon Kinlaw, is poised to step in and start in his absence.

The 14th overall pick in 2020, Kinlaw’s career has been greatly impacted by a lingering knee injury. However, he has stayed healthy in 2023 and recorded two sacks in last week’s 42-19 blowout win over the Philadelphia Eagles.

Those were Kinlaw’s first sacks since his rookie year, and both head coach Kyle Shanahan and defensive coordinator Steve Wilks responded to his performance with praise that indicated they have full confidence in his ability to fill the void left by Armstead.

Javon Kinlaw's performance against the run last week was quite different from his January display in the title game.

Crazy what being healthy does. pic.twitter.com/u95sTP2ZgI

— Nicholas McGee (@nicholasmcgee24) December 8, 2023

“I want to say almost right when we got back from our bye week, since then Kinlaw’s game has gone up each week,” Shanahan said on Wednesday.

“I think it gets better and better each week. He’s finally strung enough practice together and being healthy this season that I think he’s really starting to get into true, he is in football shape but he is starting to play enough to where he improves every time he plays now. Same with the practice field. I think he’s really helped us out and he’s taken some big steps going forward.”

Wilks was even more enthusiastic in his appraisal on Thursday.

“I know you guys heard me talk about Kinlaw back in the spring when we were talking about guys who I think are going to have a great year. I think the number one thing with him is he’s healthy, unlike he’s been in the past,” said Wilks.

This sack owes a lot to Ambry Thomas doing excellently in the physical battle at the top of the route vs. A.J. Brown and Lenoir being fluid in his turn vs. DeVonta Smith.

However, there's a lot to be said for not staying blocked, so great credit to Javon Kinlaw too. pic.twitter.com/3gvFztELnn

— Nicholas McGee (@nicholasmcgee24) December 9, 2023

“And then there’s one word that you’re alluding to, which is he’s playing consistent. He’s really been consistent these last couple of weeks. I love the way he’s playing with lower pad level. Really as we talk about all the time, trying to create a new line of scrimmage, playing on their side of the ball. Everything we do is about penetration and you can see that with him.”

In true pass sets, Kinlaw ranks 18th in pass rush win rate among interior defensive linemen with at least 100 pass rush snaps, illustrating his knack for creating that desired penetration.

The 49ers dominated the Seahawks in Week 12 on Thanksgiving in no small part because of the disruption they generated and the pressure put on Geno Smith. The challenge for San Francisco is to ensure Armstead’s absence does not create a drop-off, but Kinlaw’s under-the-radar run of strong performances should ensure the Niners still have a consistent interior rush as they look to keep pace with the Eagles in the race for the NFC’s one seed.

Final 49ers injury report for Week 14, vs. Seahawks

One starter is definitely out.