Decision ahead for 49ers on run-stopper Armstead

Arik Armstead is enjoying a career-best season, but it appears his performance hasn’t definitively answered this question: Is the 49ers defensive end worth nearly $10 million?

The 49ers picked up the fifth year of Armstead’s contract in April, which means he’s under

Sunday’s game Who:

Seattle (8-5) at 49ers (3-10)

1:05 p.m.

When: TV: Radio:

680, 107.7

Raiders:

 It’s all business for defensive coordinator in return to Cincinnati.

B7

contract for 2019 at a salary of just over $9 million. The catch: Armstead’s salary doesn’t become guaranteed until March. In other words, the 49ers can rescind the fifth-year option before that time and part with the 2015 first-round pick.

On Friday, head coach Kyle Shanahan said nothing regarding their roster was “solidified” when asked whether Armstead will be back next season. He suggested the 49ers like Armstead, but haven’t determined whether they love him enough to invest $9 million of their 2019 salary cap for his services.

“Armstead is a very good player,” Shanahan said. “There’s no doubt that I don’t want to lose him. And I don’t think anyone in this building wants to lose good players.

“Hopefully, that’ll work out. It’s not as simple as just him, though. It has to do with how you want to allocate everything. But the one thing I do know is that I’ve been very happy with how Arik has played this year.”

Indeed, Armstead, a former

No. 17 overall pick, enters Sunday’s meeting against the Seahawks at Levi’s Stadium with far fewer social-media critics than past years.

His career-high sack total (three) is modest, but he’s a huge reason the 49ers rank 12th in rushing yards allowed per game (107.8), up from 22nd in 2017, and 10th in yards per carry (4.1). According to Pro Football Focus, Armstead has the third-highest grade against the run among edge defenders, behind two Pro Bowlers, Jacksonville’s Calais Campbell and Houston’s Jadeveon Clowney.

Inside linebacker Fred Warner, who has had a good view of much of Armstead’s work, was asked about Armstead’s ability to dominate offensive linemen with his 6-foot-7, 292-pound frame.

“He can and he does,” Warner said. “He’s a big dude, and he uses his size and his strength to his advantage. He makes some plays like, ‘oooh,’ plays that jump off the tape. That’s been big for us up front.”

It’s the type of seasons some fans have been impatiently awaiting. From 2016-17, Armstead had four sacks and missed 18 of 32 games because of a torn labrum (2016) and broken hand (2017).

“He’s been getting a lot of bad pub just because he’s been hurt the past couple years,” defensive tackle DeForest Buckner said. “… But being able to stay healthy all year, he’s getting to really show everybody what he’s able to do.”

Buckner, who was also Armstead’s teammate at Oregon, is a close friend who has a sense of how being viewed as a firstround disappointment has affected him.

“I feel like he feeds off that negative energy, like most of us do,” Buckner said. “He really just keeps

49ers (3-10) vs. Seahawks (8-5) Where: When:

TV: Radio:

Spotlight on:

Levi’s Stadium

680, 107.7

TE George Kittle: He provides a compelling reason to watch a 3-10 team. Last Sunday, Kittle nearly treated the home fans to history when he had 210 receiving yards, 5 yards shy of breaking Shannon Sharpe’s NFL record for yards by a tight end. But Kittle (1,103 yards) has his sights on another league record: He needs 225 yards in the final three games to break Rob Gronkowski’s record for most receiving yards by a tight end (1,327). At his current pace, Kittle will finish with 1,358 yards, but still might not own the NFL record: Kansas City’s Travis Kelce has 1,220 yards this season through 14 games.

49ers — S Jaquiski Tartt (shoulder) is out; RB Matt Breida (ankle) is questionable. Seahawks — RB Rashaad Penny (knee) is out; WR Doug Baldwin (hip) is questionable.

Injury notes:

WHAT TO WATCH FOR

1:05 p.m.  The Seahawks have an NFL-low 10 turnovers. The 49ers have an NFL-low five takeaways, putting them on pace to break the league record of 11.

 The 49ers allowed 168 rushing yards in their 43-16 loss to the Seahawks on Dec. 2, which was the most they’d surrendered since Oct. 22, 2017.

 Seahawks QB Russell Wilson has thrown 12 TD passes and one interception and posted a 109.2 passer rating in his past six starts against the 49ers. it all inside. He doesn’t really share his feelings a lot. I know he keeps it inside and he uses it as fuel for his own fire. It’s just good to see that on Sundays.”

Armstead typically hasn’t shared his feelings too much with reporters.

On Thursday, he offered a typical response when asked about his 2018 season: “I think I’ve been doing some good things. There’s always room for improvement.”

What part of his game is he happy about? “Just being healthy. Being on the field. Being able to be a productive player.”

Armstead said he hasn’t had conversations with the 49ers’ decisionmakers about whether they’ll keep him for next season with the fifth-year option: “Just trying to control what I can control and play well.”

The 49ers hope Armstead can provide more in the sack department, but it’s worth noting that’s never been his specialty: He had four sacks in his three-year Oregon career before registering nine in his first 43 NFL games.

So is he worth $9 million if he remains a solid starter who excels as a run defender? He might be a bit overpriced, but the 49ers are projected to have $67 million in salary cap space available for next season. Last offseason, when they were also swimming in cap space, they paid defensive back Jimmie Ward $8.5 million on his fifth-year option, even though he began 2018 as a backup.

Another option is to sign Armstead to a contract extension, which would lessen his 2019 base salary. That’s what the 49ers did last offseason with guard Laken Tomlinson, instead of picking up his fifth-year option of $9.6 million.

Whatever the case, Armstead has increased his chances of being a $9 million man next season, though nothing is guaranteed.

“I still think he can get a lot better,” Shanahan said. “And hopefully it’s here with us.”

Eric Branch is a San Francisco Chronicle staff writer. Email: ebranch@ sfchronicle.com Twitter: @Eric_Branch