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It just so happens that Fred Warner, in the couple months prior to Sunday’s catastrophic ankle injury, tried to prepare the 49ers’ defense for when he might have to miss some time — a proposition that seemed unfathomable just a few days ago considering his iron man reputation.

Warner did it by making his successor at the middle linebacker position, second-year man Tatum Bethune, fill in for one of his captain’s duties even when he was still healthy.

“It’s kind of crazy,” cornerback Deommodore Lenoir said this week on KNBR. “Because Fred used to always make Tatum break down the team, so I’ve seen the leadership in him already.”

With Warner now out for what’ll be an extended period of time — he underwent successful surgery to repair his fractured ankle at Stanford this week — the 49ers are turning to Bethune to wear the defense’s one helmet with a play-calling radio in it.

That’s been Warner’s domain in 132 of 133 games since 2018, when he started the opener as a rookie and forced a fumble in his first NFL action. The only game that Warner missed came in 2021, when he had a hamstring injury during a 49ers’ loss to the Seattle Seahawks.

Now, it’s Bethune’s turn to hear defensive coordinator Robert Saleh’s play calls before relaying them to the rest of the defense. The 49ers believe that he’s ready for the task.

“Just hearing him talk, I know he’s made of the right stuff,” Lenoir said. “I have the upmost confidence in him. I feel like he’s going to do great out there.”

Physically, there is no difference between what’s demanded at the three linebacker spots anymore. The 49ers made a big philosophical change there in 2019, when Saleh was in his first stint as coordinator.

“The [strong-side] ‘backer was like 240 [pounds], long and set the edge, the [weak-side] linebacker was kind of small and fast and the [middle] linebacker was kind of in between,” Saleh said Thursday. “Then we shifted the profile to just, they’re all the same guy. Whoever speaks and communicates the best is the [middle] linebacker.

“So, in this case, Tatum is next up.”

The 49ers identified Bethune as asure-handed tackler and excellent communicator before they picked him out of Florida State in the seventh round of the 2024 NFL Draft. His speed metrics were pedestrian — that’s why Bethune was available in the seventh round — but general manager John Lynch saw intangibles that he loved.

“Tatum plays like a 49er,” Lynch said Thursday on KNBR. “He’s a run-and-hit linebacker.”

Said Saleh: “Tatum is made of the right stuff. He works the right way. He communicates the right way. He believes in his ability. This is Tatum’s opportunity.”

Bethune was actually the only linebacker outside of Warner who graded out positively in the 49ers’ loss to the Tampa Bay Buccaneers. There’s reason to believe that there actually might be more concerns about the 49ers’ other linebacker spots — Dee Winters and Luke Gifford are currently manning those — than Bethune’s position in the middle.

Gifford and Winters were the 49ers’ two lowest-graded defenders against Tampa Bay, per Pro Football Focus. Winters has allowed 51 receiving yards per game into his coverage over the past three contests after surrendering just 16 yards per game over the first three. Teams have clearly been targeting him and Gifford downfield, presenting an acute need for a 49ers’ adjustment.

A trade for a linebacker can’t be ruled out, though it’s rarely easy to acquire an impact player for the right price. The New York Jets are 0-6 and one of their linebackers, Quincy Williams, is a Saleh favorite from the coordinator’s time as a head coach there.

Warner’s injury should also widen the avenue to potential playing time for rookie linebacker Nick Martin, who’s been a healthy scratch over the first six weeks. Martin missed most of his final college season at Oklahoma State with a knee injury, so the 49ers have long been considering 2025 to be a developmental season for the speedy and strong prospect (Martin’s 26 bench press reps led all linebackers at the NFL Scouting Combine).

Only this much is clear right now in this post-Warner reality: All hands are on deck for the 49ers.

“Nick has had a great week of practice so far,” Saleh said. “It’s only been two days, so hopefully he finishes it off strong tomorrow — but I thought today was outstanding without looking at the tape. Flashed in one-on-ones, flashed on special teams, and he flashed in on team defense. He can continue to grow and continue to find ways to get better and see if he can carve out a role for himself.”

Even though Brock Purdy has returned to practice this week, it’ll likely be Mac Jones starting for the 49ers at quarterback on Sunday night against the Falcons.

There have been relatively obvious hints at practice: Jones and even Adrian Martinez have been much more involved in drills than Purdy during the media viewing window.

In fact, the division of labor seems very similar to what we saw when Purdy was limited in practice prior to the Week 3 game against the Arizona Cardinals — which Jones started.

Playing the long game with Purdy makes sense for the 49ers, especially because they were essentially forced to rush him back to close September against the Jacksonville Jaguars with Jones particularly beaten up that week. Purdy aggravated his toe injury in that game and the 49ers’ upset win over the Los Angeles Rams five days later gave them the breathing room necessary to wait for Purdy to fully heal.

This much has become even more certain following Warner’s injury: The 49ers’ narrow pathway to contention is reliant on an offensive surge — which would be represented by their logo’s move to the right in the graph below.

Purdy’s mobility is what gives him an edge over Jones — and a real chance to rev the 49ers’ offense up a couple notches.

But the 49ers will likely have to wait at least one more week for him. For the time being, they’ll have to settle for the return of tight end George Kittle, who tore his hamstring Week 1 but is set to come off injured reserve before Sunday’s game.

Kittle’s presence should give the 49ers much-needed leverage at the line of scrimmage against Atlanta’s surging defense, which impressed coach Kyle Shanahan in a swarming victory over the Buffalo Bills on Monday night.

“I see a bunch of good guys,” Shanahan said of the Falcons. “They’re all very active. They’re young. They play with an extremely good motor. Every one of them has the ability to rush the quarterback. I think their scheme and just how they coach them, their effort and everything is very good. They’re playing the right way and they’re talented.”