The 49ers have improved depth at running back, which could lead to a difficult weekly decision for coach Kyle Shanahan.

If everyone remains healthy, there is simply not enough room in the backfield -- or the 46-man game day roster -- for all of their backs to contribute.

That question kicks off this week’s 49ers Mailbag, where readers submitted their queries via Facebook:

What’s the RB situation and what kind of depth do we have? (Rex Mcneill)

Because of the movement skills a running back must possess, Jerick McKinnon faces a more challenging rehab than Jimmy Garoppolo despite sustaining his ACL injury three weeks before Garoppolo. Still, the 49ers expect McKinnon to receive clearance near the start of training camp.

McKinnon was the player around whom Shanahan figured to structure the offense last season. But McKinnon's season-ending injury brought a quick end to that plan. McKinnon remains a bit of a question mark because of his physical condition, but the 49ers have very good depth at running back:



Jerick McKinnon

Tevin Coleman

Matt Breida

Raheem Mostert

Jeff Wilson

Wilson faces an uphill climb to win a roster spot, but he showed in limited time last season that he is capable of playing at this level, as long as he holds onto the ball. He rushed for 266 yards in six games (two starts) with a 4.0-yard average to go along with 12 receptions for 98 yards.

Coleman is the odds-on favorite to be the closest thing the 49ers have to a lead back. He has history in Shanahan’s system, and he was the only player among McKinnon, Breida and Mostert to practice this offseason.

It’s difficult to envision that the 49ers will have four running backs (in addition to fullback Kyle Juszczyk) active for games. Mostert will almost certainly be one of the three running backs in uniform because he is the 49ers’ best special-teams players.

That means one of the backs -- McKinnon, Coleman or Breida -- will not suit up for regular-season games. No decisions have to be made right now, of course. This is a situation that can play out based on injuries and how the players look in training camp and early in the season.

When do you think the coaching staff finally puts their foot down and settle on the starters at safety so there can be cohesion? (Zachary Van Dyck)

There did not appear to be much question which players would start when the offseason program began. Jimmie Ward and Jaquiski Tartt were the starters, and that is more than likely still the plan for Week 1.

I do not envision Tarvarius Moore gaining so much ground in training camp that he becomes a legitate contender for a starting job to open the season. Moore, Adrian Colbert, Marcell Harris, Antone Exum and D.J. Reed give the 49ers a decent amount of depth at safety.

Who do you expect to win out the other CB spot opposite Richard Sherman assuming Verrett isn’t healthy? Have there been any surprise candidates like Alex Brown that could challenge for that spot? (Greg Threlkeld)

Ahkello Witherspoon. Definitely, Ahkello Witherspoon.

He had a very good offseason program, and appears to have a renewed vigor and more urgency going into his third NFL season. At this point, iIt’s a two-man competition with Witherspoon and Jason Verrett, who is expected to be cleared at the start of camp to compete for a starting job.

Is there a possibility of trading Armstead for a serviceable CB and if so with whom? (Ehab Elsobky)

Arik Armstead has one year remaining on his contract. He is scheduled to make $9 million this season before becoming an unrestricted free agent. I can’t see any team giving up any kind of compensation to acquire Armstead for just one season at that price.

We've seen new players to the 49ers like Kwon, Bosa and Deebo held out via preexisting injuries. How much time will it take to get up to speed when camp begins? (Jeremy Wohlfart)

Deebo Samuel has the biggest adjustment because wide receivers have a lot more to learn than inside linebackers and defensive ends.

Samuel sat out the final couple weeks of the offseason program with a hip condition. Nick Bosa had a grade-1 hamstring strain in the first week of organized team activities. Kwon Alexander is rehabbing from a torn ACL of last season.

Each of those players should be ready at the start of training camp. Basically, the team repeats all the installations of the offseason program in the first two weeks of training camp, so they will not be introduced to any new concepts. Alexander and Bosa should be able to step in immediately without much difficulty. Samuel’s head will be spinning, though.

What's the 49ers backup TE situation look like with Celek out for a while with a back injury? (Patrick Jira)

The 49ers tried to cover themselves in the event that Garrett Celek is not able to work his way onto the 49ers’ 53-man roster this season. He remains in the concussion protocol and he faces a two-month rehabilitation after back surgery. At 31, Celek might have a difficult time continuing his career.

Behind George Kittle, the 49ers added draft pick Kaden Smith and veteran Levine Toilolo. Ross Dwelley and Tyree Mayfield are also in the picture.

[RELATED: Joe Staley one of just 10 players John Lynch and Kyle Shanahan have kept around]

How are the contract status of Bosa and Deebo? (Seth Hoppens)

Nick Bosa and Deebo Samuel have not signed their four-year contracts with the 49ers. That did not prevent them from attending the offseason program, but players are not allowed to attend training camp without a signed contract.

The 49ers seemed to have few worries through the draft process about their ability to sign Nick Bosa.

A source told NBC Sports Bay Area, the decision was made at the NFL Scouting Combine. Chief negotiator Paraag Marathe told Bosa’s representation in February that if Bosa did not go No. 1, the 49ers would select him at No. 2.

The terms of Bosa’s four-year contract will be $33.55 million guaranteed. The only points of negotiation are offsets and the schedule for how the money is paid out. Nick Bosa has the same representation as his older brother, Joey, and Joey signed his initial contract in late-August of 2016 to end a lengthy stalemate with the Chargers. (The contract situation did not hurt Joey Bosa, who was named NFL Defensive Rookie of the Year.)

Samuel is the only other 49ers draft pick who remains unsigned. A year ago, second-round pick Dante Pettis was the last 49ers draft pick to sign. His deal was not completed until the eve of training camp.