SANTA CLARA, Calif. -- The many injuries to hit the San Francisco 49ers defense have been well-documented, none more so than the torn Achilles inside linebacker NaVorro Bowman suffered. And while Bowman's absence has made the Niners' defensive issues, especially stopping the run, more glaring, the lack of a big bodied run-stuffer at nose tackle has gone largely overlooked.

Before the 49ers even started training camp, nose tackle Ian Williams' season was over because of an ankle injury. To replace him, the Niners hoped that veteran Glenn Dorsey would be back from a torn ACL. While Dorsey has remained on the 53-man roster all season, his return has really been nothing more than a series of stops and starts.

Dorsey didn't play in Week 1, then returned to play 15 snaps in Week 2, 17 in Week 3 and 11 in Week 4. Dorsey sat out in Week 5 against Arizona, in part because of the short turnaround for a Thursday night game, then played 19 snaps against Buffalo in Week 6 before sitting out last week's game against Tampa Bay.

"Dors just couldn't go," coach Chip Kelly said. "Later in the week, he felt like his leg was bothering him a little bit, tried to see what he could do on Sunday morning and couldn't go. And I think Dors also knows as a professional, we can't have a guy up, when you only have 46 guys up on game day, that can only go for a couple plays in the first quarter. Then, we're depleted a little bit from a line standpoint. So, felt like he couldn't give everything he had to give at that point in time. So, really his call with Ferg in terms of that he couldn't go and couldn't give us everything he could yesterday. So, we're hoping this time off will give him an opportunity when we come back for the Saints game."

According to Kelly, there were no set expectations for Dorsey from the beginning because every player who has a similar knee injury has a different way of bouncing back.

"Everything ACL I've ever dealt with in my career, and I'm not a doctor or anything, has all been different," Kelly said. "So, I don't think you can put, 'Hey, this ACL's like that.' Adrian Peterson came back after whatever and started and played really well with it. Other guys it's taken a little bit longer. But, there's more than when you look at each individual player, it could be more than that, that they have meniscus with it, was there a bone bruise in it. I don't know the exact specifics of that. So, what I've learned with ACLs is you take them all as an individual and you just can't say, 'Hey, this is the concrete. It's this. So, it becomes this amount of time.'"

Dorsey's absence has been particularly noticeable in tandem with Williams' injury. The Niners went from having what seemed like good depth for the middle of their base 3-4 defense with the likes of Williams, Dorsey and Mike Purcell to leaning on Purcell and Quinton Dial to handle the nose tackle duties. Purcell started the opener and the Niners shut down the Rams but they've been run on at will since. Dial has done what he can but is probably better suited to playing one of the other spots on the line.

The Niners haven't just missed Dorsey's production and ability to take on multiple blockers, either. He's the standing veteran on the defensive line and can provide another voice of guidance to young line mates like DeForest Buckner and Arik Armstead.

"I know he's the leader of that group," Kelly said. "It is a young group, but I think that they voted him the leader at that position. So, I feel like he adds some leadership from that and him not being out there to provide that for them, it would help the young guys. But again, the one thing with Dors is he's going to tell you what he can do and what he can't do and he's not going to fake it."