'Macho' Camacho -- 'Very, Very, Very, Very Critical'

7:49 AM PT -- The man who was killed in the shooting has been identified as 49-year-old Adrian Mojica Moreno.

Law enforcement tells TMZ ... Adrian and Hector were childhood friends. Adrian was not involved in the sport of boxing, but we're told he was big into cockfighting.

Boxing legend Hector "Macho" Camacho went into cardiac arrest after being shot in Puerto Rico last night ... and doctors say "the prognosis is not good."

Camacho was hit several times in the face and neck in a drive-by shooting outside of San Juan ... and was immediately rushed to a nearby hospital.

A rep for the hospital told reporters, "The situation with 'Macho' is very delicate ... his physical condition will help him but we will see."

The rep added, "[Camacho] went into cardiac arrest. The doctors were able to get his heart started again with the medicine and we are maintaining his blood pressure and pulse stable medically right now to see whether during this morning, afternoon or evening we see a positive change."

Camacho was a passenger in a Ford Mustang when the shooting happened. The driver of Camacho's car was killed in the attack.