Dr. Ernesto Torres, medical director of Rio Piedras Medical Center in San Juan, Camacho was breathing through a ventilator but had not been declared brain dead, the Puerto Rico newspaper Primera Hora reported.
"He is in a deep coma," Torres told reporters. "The bullet damaged three arteries that run through the neck, so the blood is not arriving at the brain."
The doctor said tests on the 50-year-old winner of super lightweight, lightweight and junior welterweight world titles would continue.
"His mother already knows that the prognosis is not good and we have said she has to be prepared for the worst-case scenario," Torres said. "We will continue doing tests tonight and tomorrow morning at the request of one of the emergency doctors."
San Juan Police sad Camacho was severely injured and a companion killed Tuesday while they were sitting in a car near a shopping center in the city.
Authorities said one or two men got out of a sport utility vehicle, walked over to the parked car and opened fire, killing a man identified as Alberto Mojica Yamil Moreno and seriously wounding Camacho.