The San Francisco 49ers have been bitten by the injury bug on defense during the second half of the season.

San Francisco's defensive front and secondary have taken hits in recent weeks and the 49er will be missing starters in both areas on Sunday as they look to bounce back from their Christmas Day defeat to the Baltimore Ravens.

Defensive tackle Arik Armstead has been ruled out for a fourth straight game with foot and knee injuries, while rookie safety Ji'Ayir Brown, who has filled in impressively for Talanoa Hufanga at safety after the All-Pro tore his ACL in Week 11, is unavailable because of a knee sprain.

Confidence in Ryan

The 49ers have made veteran additions at both spots this month. They signed two-time Super Bowl champion Logan Ryan for depth at safety and nickel on December 6 and this week brought in Sebastian Joseph-Day, a Super Bowl winner with the Los Angeles Rams in the 2021 season, at defensive tackle.

Both players are set to feature as the 49ers visit the Washington Commanders in a game where they will at least look to preserve their advantage in the race for the NFC's one seed.

Ryan, who has played sparingly on defense to this point, is poised to start next to fellow veteran Tashaun Gipson at safety.

Asked what gave him confidence in Ryan's ability to step in, Shanahan replied:

"Just us playing against him. He always seemed like such an aware, smart player and a guy that had a lot of experience playing a lot of different defenses. We brought him in here when we had a few injuries. He looked just since he’s been here like what we hoped he was. Now that we’ve had those injuries, he is in that role. He’s looked exactly like we hoped he’d be. He’s very comfortable and knows what he’s doing and the game’s not too big for him.”

Joseph-Day's challenge

It's unclear what Joseph-Day's role will be given the little time he has had to adapt to the defense. Joseph-Day, as defensive coordinator Steve Wilks pointed out on Thursday, has played as a two-gap defensive lineman during his career but now joins an aggressive one-gap front.

"We come off the ball here," said Wilks. "So, I like his explosion and how he comes off. He plays with violent hands, so I’m excited to have him and looking forward to seeing what he can do for us."

Joseph-Day, prior to being released by the Los Angeles Chargers as part of their imminent rebuild, was enjoying his best season as a pass rusher with three sacks and 11 quarterback hits. 

And Shanahan clearly believes the former division rival can have an immediate impact.

"He’s looked great in our three practices, even though only two periods of them were full speed," said Shanahan. "But I mean, he looks like the guy we’ve gone against. I expect him just like all these other vets, he’s going to get in, he’s going to try to make plays, try to do his job and help us contribute to the rotation of our group."

The injuries to Hufanga and backup and key special teamer George Odum forced the 49ers to look for outside help at safety, but Shanahan was asked more broadly about whether it's an organizational philosophy to have veteran backups on the roster who might be better prepared to play than a younger player they have been developing.

He responded:

"Our just overall philosophy is in that given day, in that given week, in that given season, what gives you the best chance to succeed? It might be the younger guy. It might be the older guy. I think it’s very wrong when you take an absolute philosophy to anything. Like, ‘hey, you’ve always got to give the younger guy the first shots because he needs that experience and that’s how you develop him.’ That’s great, but not at the expense of the other 52 guys on the team and the organization and losing games. The first decision always is what helps you win the most or gives you the best chance to win. In a league that it’s very hard to develop guys because when you do anything at a professional level, it’s hard to do it at extremely high level when you’re not working on it year-round. So, those guys who really can play in the NFL are usually guys that have experienced the NFL. They know how to handle those situations."

With injuries hitting hard, the 49ers are betting Ryan and Joseph-Day can handle the situation effectively in a game San Francisco must win to at least stay in the one seed going into the final week of the regular season. 

Should the veteran duo succeed, the Niners' approach to their injury issues will look very smart.

49ers injury report gives Brock Purdy great chance of a happy new year

Great news for the offense.