Bill Goldberg -- I Don't Respect Donald Trump ... Because He Fired Me

Bill Goldberg says he lost all respect for Donald Trump back in 2010 -- saying he's still pissed about the way he was fired from "The Celebrity Apprentice."

The firing was especially nasty ... but at the time, most people just chalked it up to reality show editing. Turns out, the anger was REAL.

"I respected him a lot before he fired me," Goldberg told TMZ Sports.

There's more ... Bill says Trump is basically the same person as WWE honcho Vince McMahon -- "They're both kind of off their rocker."

FYI -- Bill doesn't like Vince either.