Jude Alcala, who worked with the rock matriarch on the hit programme in 2012, is suing producers behind the reality contest and NBC network bosses for negligence, after breaking his thigh bone and damaging his shoulder in a stage fall.
The injuries required surgery and Alcala is now demanding unspecified damages from the defendants for failing to place proper warning signs around the stage.
Now Osbourne, who quit Agt as a panel judge last year (12), has taken aim at show bosses on Alcala's behalf, declaring the studio had "the worst stage in the entire world" and expressing her disgust at producers' failure to lend their support to the make-up artist after the accident.
She tells Tmz.com, "The guy's been sick for over a year, I think it's a disgrace they ignored him. He's had an operation but he's been in and out of work for the past 18 months...
"Some guy designed a stage set with a hole in the middle. Somebody has to pay the price."