Buffalo Bills running back Fred Jackson could miss two weeks after suffering a hamstring injury at practice on Friday.

Jackson suffered the injury midway through the practice session and didn't return. The 34-year-old is Buffalo's No. 2 running back behind starter LeSean McCoy.

Bills coach Rex Ryan says Jackson's injury is "not a terrible one," but he will probably miss two weeks.

Jackson has been one of Buffalo's top contributors on offense over the past eight seasons. The injury further depletes Buffalo's depth at running back; backup Anthony Dixon is expected to miss up to a month with a calf injury.

With numbers low at running back, the Bills signed undrafted free agent Bronson Hill on Thursday.