The 28-year-old sustained a spinal contusion after attempting a tackle against the Cincinnati Bengals on December 4, 2017 ... and many feared he would be permanently paralyzed from the waist down.

Shazier defied the odds and worked like crazy to rehab following the incident ... slowly improving his mobility over the course of the following year -- and was eventually able to deadlift and jog.

The Pro Bowler has moved on from his dream of returning to the field for new endeavors on Wednesday ... announcing his decision in an emotional video.

"When you play the game of football the way I did, you convince yourself you're Superman. That nothing can stop you," Shazier says.

"But then the moment I got hurt, I stopped being Superman and that was difficult to make sense."

"But, the way I look at it, God put us all here for a purpose. For 20 years, he let me play football and now its time for me to do what he wants me to do."

"I'm gonna step away from the game for a while and see what else life has to offer. I know football will always be here for me if I need it but right now I'm excited to explore new challenges and different paths."

Shazier hints he won't be stepping out of the public eye ... and promises to reveal details about his next project soon.

The linebacker goes on to thank all the coaches, fans and doctors who supported him throughout his rehab process ... and showing how much they care about him off the field.

"When I got hurt, football may have been taken away for me, but everything it gave me is still here inside."