The Pittsburgh Steelers announced on Thursday that Ryan Shazier underwent surgery to stabilize his spine, but it is unclear when the star linebacker might return to the field. According to one doctor, there’s a chance it may never happen.

Dr. Anthony Alessi, a neurologist from the University of Connecticut who consults with the NFL Players Association, told ESPN’s Michele Steele that the type of procedure Shazier underwent could indicate his playing career is over.