Buffalo Bills head coach Rex Ryan informed the assembled media Monday morning that injured safety Aaron Williams has entered concussion protocol.

Williams was injured in a collision with a teammate at practice on Thursday.

The five-year pro underwent neck surgery in 2015 after jamming his neck during a play in Week 2 of last season. He has since said he has no worries about re-injuring the neck, however.

Williams was penciled in as the team's starting strong safety ahead of its first preseason game. He'll have to pass a series of tests before he is allowed to return to the field.