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

Injuries have sidelined five Cleveland backs in the first week of training camp, preventing the team from working on its rushing game and forcing the Browns to use two defensive players at fullback during practices.

One of the injured backs is rookie Duke Johnson, a third-round pick from Miami expected to have a huge impact on Cleveland's offense this season. Johnson missed his third practice Wednesday with a pulled left hamstring and it's not clear when he will return.

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Coach Mike Pettine expressed some frustration and disappointment with the rash of injuries. The Browns plan to emphasize the run under first-year coordinator John DeFilippo, and any time missed by players, especially young ones, makes it harder for them to learn the system.

Also, Terrelle Pryor, attempting to switch from quarterback to wide receiver, sat out with a hamstring issue.

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