Frank Cascio - who later became the star's manager - says the King of Pop first took propofol after a fall on stage in Munich, Germany.
He claims in his memoir My Friend Michael: An Ordinary Friendship With An Extraordinary Man that Jacko was also using the drug ahead of his 30th anniversary concerts in 2001 - causing the shows to be delayed.
“My naive belief that Michael wouldn’t let his medicine interfere with the show blew up in my face,” Cascio writes in the book.
“I can’t begin to describe my disappointment and panic at that moment.”