BEREA, Ohio (AP) — The Browns are running low on running backs.

Six practices into training camp, they’ve lost five backs, including Terrance West, the team’s leading rusher in 2014, and touted rookie Duke Johnson, with injuries. On Wednesday, the Browns were so short-handed in the backfield that they used two defensive players at fullback during practice — not exactly the plan.

As the injuries mount, coach Mike Pettine’s weariness grows.

“It is a source of frustration when you have limited (players),” he said, “and when it starts to pile up at a position, you have a ripple effect that starts to effect the other guys and their repetitions. And then you have to look at the overall picture of practice and cut down on reps, and there are guy at other positions that need reps.

“Sometimes the consequences of it are frustrating.”

Johnson, a third-round pick from Miami, missed his third straight practice with a pulled hamstring. It’s not known when he’ll be back, but what’s clear is that every day he’s out costs him valuable experience — and a chance to get more comfortable in first-year coordinator John DeFilippo’s offense and with one of the NFL’s best lines.

The Browns will emphasize running the ball this season, and the team sees Johnson as a player they can use in a multitude of ways. But not while he’s on the sideline. As their teammates worked out on a beautiful sunny morning, West (calf) and Johnson rode stationary bikes and then stood and watched.

“It’s just disappointing that a guy that we’re counting on to be a big part of what we do, to lose him at this formative time of what we’re getting done, that’s tough,” Pettine said. “He’ll have a lot of catch-up work to do. We’re making sure he gets all of those reps mentally. But there’s no substitute for actual live reps.”

Along with losing West and Johnson, the Browns’ bruised backs include Glenn Winston (knee) and fullbacks Malcolm Johnson (shoulder) and Luke Lundy (concussion).

On top of those injuries, former Oakland quarterback Terrelle Pryor, who is attempting to switch to wide receiver, sat out with a tight hamstring. Linebacker Barkevious Mingo missed practice with a knee injury. He played last season despite a serious shoulder injury that required offseason surgery.

Also, receiver Dwayne Bowe (hamstring) and defensive lineman Billy Winn (ankle) were out.

Pettine said he’s leaning toward Pryor being “doubtful” for the team’s scrimmage Friday at Ohio Stadium in Columbus, the former QB’s first visit to the school since he left amid an NCAA investigation into a tattoos-for-memorabilia scandal involving several Buckeyes players in 2011.

If there is any positive to the injuries, it’s that they are allowing Isaiah Crowell, who ran for 607 yards and eight touchdowns last season, and Shaun Draughn, signed late in 2014, to show what they’ve got. In addition, the team signed running backs Jalen Parmele and Timothy Flanders earlier this week for depth.

With bodies at a premium, Pettine now has to worry about overworking his healthy players.

“We don’t want to overuse those guys,” Pettine said. “I think Shawn certainly benefits from it a lot, and Crow needs every rep he can get just being Year 2 in the NFL. But Year 1 in a new system, where the pass protection stuff is a little bit different and involving the running backs more in a pass game, he needs all of those reps.”

There’s plenty of time for the Browns to get healthy, but this early rash of injuries is concerning because of the quantity and quality of players involved.

“I know it’s a part of camp, but that’s something we try to prevent,” Pettine said. “We really stress being proactive with it, getting the sleep, the hydration, the nutrition. We evaluate how we do things all the time. When that number starts to get above what the norms are, then that’s an area for concern and that’s something as an organization that we’re looking to address.”

NOTES: With FBs scarce, LB Scott Solomon and DL Dylan Wynn were used as lead blockers in a hard-hitting goal-line drill won by the defense, which earned the right to wear camouflage jerseys on Thursday. … Backup QB Johnny Manziel had a solid practice, completing several nice throws including a 60-yard TD to rookie WR Darius Jennings. … Another rookie, WR Shane Wynn, a Cleveland native who played at Indiana, hooked up with QB Josh McCown for a long TD.