Osbourne is said to have called Gaga vile, a bully and a hypocrite in her new autobiography.
Osbourne has claimed that Gaga had encouraged her fans to torment her daughter Kelly, 28, with online abuse. This has not gone down well with Gaga, reports dailystar.co.uk.
Gaga, 27, reportedly hit back saying that she was "in no mood" to be in the same building as Osbourne, said the former's friends.
"Sharon didn't hold back in her comments and there is now a very real concern Gaga might just pull out of the show," said a source.
However, producers are ready to take extreme measures to keep Gaga's performance on track.
"I am sure we will be doing all we can to make Lady Gaga feel welcome," said a source close to show bosses.
--IANS (Posted on 04-10-2013)