SANTA CLARA -- Running back LaMichael James was carted off the field Sunday after he suffered an injury to his left arm early in practice.
NFL Network reported that James suffered a dislocated elbow and that he is expected to miss a month or so.
James had just become a top contender for the No. 2 running back role Friday, once Kendall Hunter went down with a torn anterior cruciate ligament in his right knee.
It's believed James got hurt in a pass-blocking drill. Coach Jim Harbaugh hovered over James on the ground before a trainer whisked James off to the locker room in a motorized cart.
James appeared to be supporting his left wrist with his right hand. The 49ers did not provide any information on James' injury.
James spoke Saturday about how he approaches pass protection, stating: "It's more of a mental game. Eyes in the right spot. Picking up blitzes. Now this is my third year, and I have a better grasp of anything."
Injuries have struck James leading up to his two previous NFL seasons. James sprained his left knee in the 49ers' 2013 exhibition finale at San Diego, and an ankle injury required him to be carted off the field in a 2012 exhibition at Houston.
Running back was one of the 49ers' deepest positions entering camp. Now, rookie Carlos Hyde and former practice-squad player Jewel Hampton are the only healthy backups behind starter Frank Gore.
Marcus Lattimore eventually will join that group. He began camp on the non-football-injury list while conditioning his reconstructed right knee.
"There's a percentage that it needs to get better," Harbaugh said of Lattimore's knee. "As I watched him through the offseason, you could see it getting better every single day. ... It's not yet 100 (percent)."
After Hunter's injury, James said Saturday: "I know everybody is looking at me now. I'm going to go out there and work hard."
Last season's knee sprain caused James to miss the first three games of the regular season, and Harbaugh said it ultimately affected James' spot on the depth chart.
James took over as the 49ers punt returner the second half of the season. He had only 12 carries for 59 yards in the regular season and one rush for no yards in the NFC Championship game loss at Seattle.
Before Sunday's practice and James' injury, Harbaugh gave James a strong endorsement:
"We have complete and total confidence in LaMichael James," Harbaugh said, "and I don't see anything (needed) in terms of stepping up or proving anything on his part. We know him to be a very fine football player."
Staff writer Steve Corkran contributed to this story.