Coach Rex Ryan said after practice that the team was not yet sure about the severity of Ragland's injury, but didn't believe the team's second-round pick tore any ligaments.
Ragland, who was pursuing running back Reggie Bush toward the sideline, pulled up limping and immediately went to the ground.
"It just looked odd," Ryan said. "It wasn't hit. None of that stuff. So sometimes those can be the worst ones, so I'm hoping -- we just have to keep our fingers crossed and hope he's fine."
The Bills traded up to select Ragland with the No. 41 overall selection. General manager Doug Whaley said the team considered selecting the Alabama linebacker with its No. 19 pick in the first round, but Buffalo drafted Clemson defensive end Shaq Lawson instead.
Lawson is expected to miss the first several games of the regular season after undergoing shoulder surgery this spring.
Ryan had already named Ragland as the expected starter at inside linebacker alongside Preston Brown. Veteran Zach Brown replaced Ragland with the first-team defense for the remainder of Friday's practice.
"I'd rather not think about it, but we're in the capable hands," Ryan said of the possibility of losing Ragland for an extended period. "We have a couple of pretty good inside 'backers, guys that are doing well right now -- Zach Brown and Randell Johnson -- so one guy would have to step up."