"Britney will get the boot," a source toldUs Weekly in its latest issue. "Producers wanted her for the long haul, but it isn't working."
Spears apparently lacked the stamina the show's producers were looking for from its rookie mentor, especially since the pop star had been signed to a $15 million contract for The X Factor's recently-concluded second season.
"They paid all that for her to say 'amazing' and offer half-claps," a second source told the magazine.
Added a show insider close to The X Factorco-creator and judge Simon Cowell, "Simon wanted crazy Britney, but he got boring Britney."
Earlier this month, Cowell told E! News that Spears' participation would depend on how busy the singer's schedule is.
"I don't know yet, to be honest with you. I haven't had the conversation with her whether she'd want to, what other commitments she's got," he explained.
Although seemingly noncommittal, Cowell said he would probably like Spears to return.
"Yeah, I think I do, yeah. But like I said, and it goes back to L.A., it all depends on how much time they can give us," Cowell told E! News, referencing how veteran judge L.A. Reid recently confirmed his own departure from the show.
Spears had said she planned to return to The X Factorduring an interview last month.
"Yes, I definitely will," Spears told Rollingstone.com at the time.