Ex-NFL star Deltha O'Neal broke his back and neck in a horrific car crash in August ... and now, prosecutors have hit the former DB with DUI after they say he was drunk during the fiery wreck.

According to court docs obtained by TMZ Sports, O'Neal and a passenger were on their way home from a Royal Palm Beach, Fl. bar on Aug. 7 when O'Neal lost control of his Mercedes.

Witnesses say the scene was wild ... claiming O'Neal's ride hopped a curb, slammed into a utility pole, ripped in half, skidded into trees and caught on fire.

According to the docs, O'Neal and his passenger were SERIOUSLY hurt ... with Deltha suffering a broken ankle, fractured back and neck, concussion, eye injury, brain bleed and an intestine injury.

The passenger, meanwhile, suffered even worse trauma ... with the docs saying the guy needed a 16-INCH ROD to repair a broken femur caused by the crash.

Cops say after the two were transported to the hospital ... O'Neal reeked of booze -- and when they got his blood tests back, one of the results revealed O'Neal's BAC was .195.

Cops eventually issued a warrant for his arrest ... and, according to Miami jail records, ultimately picked up the 42-year-old earlier this month.

O'Neal -- who admitted to having a few beers before the crash -- has been hit with two counts of DUI ... and is due in court next month to face the charges.

O'Neal was a STUD for years in the NFL ... recording Pro Bowl appearances in 2001 with the Broncos and in 2005 with the Bengals.

In his 9-year career, Deltha record 34 interceptions and 389 combined tackles.