The Denver Broncos lost their top two running backs in Sunday's opening full-camp practice. They were Knowshon Moreno and Correll Buckhalter.Knowshon Moreno twisted awkwardly as he attempted to catch a pass along the sideline in a seven-on-seven drill, then was carted off the field. Moreno couldn't put any weight on his right leg and was aided by two trainers into the team's facility. The fear is that Moreno tore his hamstring, which would sideline him for at least the rest of camp.Shortly afterward, backup Correll Buckhalter walked off the practice field holding his lower back. It's unsure when he'll be able to practice again. And coach Josh McDaniels refused to answer questions about the injuries Sunday night.Without Moreno and Buckhalter, Kolby Smith and Lance Ball will get added carries. Having traded J.J. Arrington last week, the Broncos might reconsider signing free agent Brian Westbrook.