Detroit Lions safety Tracy Walker III sustained a possible left Achilles injury during Sunday's 28-24 loss to the Minnesota Vikings.
Walker injured his lower left leg during a no-contact situation in the first quarter. After being helped to the sideline, Walker soon was taken to the locker room on a cart.
Detroit coach Dan Campbell said the club will have a better idea of the injury after further evaluation.
"We don't know entirely," Campbell said. "We'll know more in the morning. It doesn't look real good, but it's obviously the ankle area, possibly could be the Achilles. We'll see."
Losing Walker, a team captain, would represent a big blow for the Lions. The fifth-year pro, who is 27, accumulated a career-best 108 tackles last season before re-signing with Detroit on a three-year, $25 million deal.
JuJu Hughes replaced Walker and had a career-high eight tackles in Sunday's game.
Hughes, 24, said he is ready for increased duty should Walker's injury prove to be of a long-term duration.
"This is what I've prepared for, this is what I'm here for, this is the dream I've always wanted," Hughes said about the opportunity. "God, you hate to see someone like (Walker) go down, especially a leader of your team, a leader of our secondary, but, you know, it's next man up in our room. That's me. I've gotta step up and be ready to fill that role and play to my abilities."