The 40-year-old has checked to rehab to tackle a substance abuse problem, meaning that he will not be involved in the blockbuster bout in Las Vegas this weekend.
"He actually called me on Monday afternoon and sounded terrible," Schaefer told Sky Sports News. "He told me he needed help, that he can't go on. I put him in touch with the proper people and they helped him get into a rehab facility for substance abuse.
"Obviously the timing isn't good during the biggest fight week in the history of boxing, but when you have an illness it's not like you can choose the timing. When you need help you need help and of course I'm supportive of that because health and life and family comes before everything else.
"I sure hope on behalf of myself and the Golden Boy team and the Mayweather team and fight fans around the world that he gets the help he needs."
De la Hoya first checked into rehab in May 2011.