The America's Got Talent judge took aim at Cowell during a US television appearance this week, suggesting that he suffered from "small penis syndrome".
At the time of her comments, which were made in the wake of a series of revelations about Cowell's private life, Osbourne joked that he would "probably fire [her] now".
According to The Mirror, sources say that Cowell now "knows who his real friends are", and is considering axing Osbourne from America's Got Talent.
"Simon doesn't want anything to do with Sharon ever again," an insider claimed. "He thought he could rely on her to be supportive when the chips were down.
"She has come out with all kinds of accusations and the new series of American's Got Talent will be her last. Simon cannot have people working on his show who he does not trust."
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Watch the Britain's Got Talent judges talking to Digital Spy about Simon Cowell's return to the show: