The San Francisco 49ers will likely be without running back LaMichael James for the next month or so with a dislocated elbow. A month's absence means he should be back in time for Week 1 or 2 of the regular season, although complications could always slow that down.
The 49ers still have four preseason games to play, and right now, their healthy running back contingent includes Frank Gore, Carlos Hyde, and Jewel Hampton. Gore is unlikely to get many carries in the preseason, if any at all. Right now, that means Carlos Hyde and Jewel Hampton are splitting a bunch of carries. While I suppose the team could figure out some way to make that work, I have to think the team signs a running back to serve as a camp body. This would be a guy who has virtually no chance of making the 53-man roster, but rather is able to just take carries. And given the 49ers depth, it could be a chance to impress a team with less depth at running back.
The return positions will be a question mark as well, but the 49ers have guys they will roll out to see what they can do. Bruce Ellington in particular will get plenty of work as a return man. We'll do some more research into that, but for now, I think having a camp body at running back is the bigger deal in the short term.
I did some poking around, and came across some lists of free agent running backs. One or two of these guys might have since signed, but I believe all of them are currently available. It is important to note that this does not include rookie free agents. If anybody has a link to a list of available UDFA running backs, let me know in the comments. You can go through this list of running backs at ESPN, but it just lists all draft eligible running backs.