Howard Stern is unloading on Novak Djokovic over his COVID-19 vaccine drama ... calling the tennis superstar a "d****bag," "f***ing a**hole," and a "f***nut" in a fiery rant.
34-year-old Djokovic has been fighting like hell to compete in the Australian Open this month despite the country's strict COVID-19 mandates -- he initially had his visa canceled after authorities claimed he did not meet requirements for a vaccine exemption ... before that decision was overturned on Monday.
Stern -- who's gone after sports stars like Kyrie Irving and Aaron Rodgers for their vax stances in the past -- sounded off on the Joker during Monday's episode of "The Howard Stern Show" .