Osbourne and Gaga fell out in January 2013 when Ozzy's wife labelled Gaga's Little Monsters 'hideously violent' after a feud between the singer and Kelly Osbourne.
The row has been again discussed in Sharon Osbourne's new autobiography, which is released on 10 October, in which the rock and roll matriarch describes Gaga as a "bully" and "hypocrite".
Now, Gaga's planned performance on X Factor is believed to be in jeopardy.
"Sharon didn't hold back in her comments and there is now a very real concern Gaga might just pull out of the show," says a source for the show to The Daily Star, and producers are planning to pre-record Lady Gaga's performance before Sharon Osbourne arrives at the studios.