EXCLUSIVE

A Dallas high school employee claims Deion Sanders' teenage son brutally attacked him on school grounds ... beating him so badly, he needed spinal surgery ... this according to court docs obtained by TMZ Sports.

The alleged victim is John Darjean -- who claimed Sanders was breaking school rules in Sept. 2015 by using his cell phone on campus during school hours ... and he tried to confiscate the phone.

But instead of handing it over, Sanders allegedly got violent -- giving Darjean serious enough injuries that he was transported to a local hospital ... and later needed spinal surgery.

The insurance company that paid out his workers comp claim is now suing Deion and his ex-wife Pilar -- claiming they knew their son had a history of reckless conduct and never did anything to curb his behavior. The insurance company claims Deion and Pilar should reimburse them for the $26k payout.