The follow-up tweet gives a clearer indication of the potential seriousness of the injury:
Hopefully this was all done in time to save his ability to walk.Alessi says surgery is needed when the “bones around his spinal cord are dislocated. This is a more severe injury (than a contusion.)”
“This is a much more severe situation on our hands than we thought.”
— Michele Steele (@ESPNMichele) December 7, 2017
Also given this situation, I wonder if Shazier's flipping himself over after the injury did him more damage. There have been other situations where the medical people strap a board to a guy and then flip him over so the possibly damaged spine doesn't get injured further.