The late 'Thriller' singer's hair was accidentally set on fire as he was making an advert for soft drink Pepsi in 1984, and his pal believes the subsequent treatment he received following the accident sent the star - who died of acute Propofol intoxication in June 2009 - into a downward spiral.
Speaking on BBC Breakfast, David said: "When he started his solo career and he left Motown, when he did 'Off The Wall', 'Bad' and 'Thriller', he was in complete control of everything he did. He was in charge.
"It was that accident, when you get a head concussion it changes your life because you get addicted to drugs, to get rid of all the pain, and that started with filming that commercial."
As a result of the accident, Michael was rushed to hospital and treated for second degree burns. He likely had plastic surgery soon after to hide his hair loss and altered his appearance many times over the rest of his life, with David claiming he had to undergo 'ballooning' procedures, a method of alopecia reduction for surgical hair restoration, up until he died.
He added: "He never got over that. He had ballooning, ballooning is when you expand the scalp, until the day he died he was being ballooned."
Michael's brother, Tito - who also appeared on the show - said Michael was "dropped something like 40 or 50 feet from the stage at one of his shows," which also had a bad effect on him.
David's documentary, 'Michael Jackson: The Life of an Icon' will have its London premiere on Wednesday (02.11.11), and is available to buy on DVD now.
Michael's personal physician, Dr. Conrad Murray, is currently on trial for the involuntary manslaughter of the singer.