The San Francisco 49ers might have a problem in one of their key position groups.

During the John Lynch-Kyle Shanahan tenure, the 49ers have built their defense from front to back. That means they've prioritized a stout defensive front that gets after the quarterback. Everything else with their defense falls into place after that.

While the club has improved in the secondary and frequently rolls out the best linebacker duo in the NFL, their defensive line is in a tough spot heading into the second week of the preseason.

Depth has been one of the calling cards for their good defensive lines. They're not only a top-heavy group with players like Nick Bosa and Javon Hargrave, but they've consistently had good depth behind their starting units.

Last season their depth struggled. They made two in-season trades for defensive ends and never found enough quality to go behind Hargrave and his fellow defensive tackle Arik Armstead. As a result, the 49ers pass rush wasn't as impactful as we're used to seeing and their run defense faltered down the stretch.

This offseason they shuffled things up.

Armstead was released. In his place the 49ers added free agent DT Jordan Elliott, and traded for former Houston Texans DT Maliek Collins.

At defensive end Randy Gregory and Chase Young both left in free agency, clearing the way for free agent additions Leonard Floyd and Yetur Gross-Matos.

A starting group of Floyd, Bosa, Hargrave and Collins is solid. Gross-Matos is a versatile reserve, and Elliott is putting together a nice camp. Former undrafted free agent Kevin Givens also figures to be in the rotation.

Outside of that, things are dicey for the 49ers. They have enough bodies at defensive tackle that they should be able to find a good rotation, even after a knee injury that will sideline DT Kalia Davis for half the season. Defensive end is a different story.

Drake Jackson was supposed to be a key role player, but his season is already over due to his ongoing recovery from offseason surgery. Second-year DE Robert Beal Jr. should have plenty of opportunities after playing in just four games as a rookie. He played 51 total snaps in the 49ers' preseason opener against the Tennessee Titans and had a couple of run stops, but he didn't post a pressure in 24 pass rushing snaps according to Pro Football Focus.

The only DE that did post a pressure for the 49ers against the Titans was veteran Alex Barrett who has been a practice squad staple the last four years. Barrett doesn't figure to be in the team's plans beyond internal depth.

Recently-signed DE Jonathan Garvin had an okay game after not getting much time to practice. Garvin was a seventh-round pick of the Green Bay Packers in 2020. He had 1.5 sacks in 38 games with the Packers before his release in 2023. His track record doesn't indicate he'll be a major factor for the 49ers this year.

This is a vital group for the 49ers and they don't have a ton of depth to withstand either a subpar showing or an injury. Their margin for error is razor thin at a position they've prioritized consistently during the Lynch-Shanahan era. Don't be surprised if there's a trade in the works either before the season or during the season to improve that unit.

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This article originally appeared on Niners Wire: Big problem brewing at one of 49ers most important position groups