The fighter's last title bout came against then-welterweight champion Oscar De La Hoya in 1997, when he lost on a unanimous decision after winning super lightweight, lightweight and junior welterweight world titles in the 1980s.
Camacho, 50, was rushed to San Juan's Centro Medico trauma centre in Puerto Rico after the shooting, where he was in critical but stable condition.
Adding to the complications, Camacho suffered a heart attack and doctors described his brain activity "rather low".
Camacho's spokesman Steve Tannenbaum was upbeat though and said: "This guy is a cat with nine lives. He's been through so much - if anybody can pull through, it will be him."
Tannenbaum claimed Camacho was going to fight two years ago in Denmark until his opponent pulled out - but they were still looking at a possible bout in 2013.
"We were talking comeback even though he is 50 - I felt he was capable of it," he added.
In his prime the Peurto Rican fought high-profile championship bouts against Felix Trinidad, Julio Cesar Chavez and Sugar Ray Leonard, whose career he ended with a 1997 knockout.
Camacho had a career record of 79-5-3, with his most recent fight coming in 2009.
He has battled drug, alcohol and other problems since and was sentenced in 2007 to seven years in prison for the burglary of a computer store in Mississippi.
However, a judge eventually suspended all but one year of the sentence and gave Camacho probation. He served only two weeks in jail.