The 'Circus' singer joined LA Reid and Demi Lovato for the Kansas City auditions over the weekend, with X Factor UK judge Louis Walsh filling in for an ill Simon Cowell.
The X Factor judging panel discussed the potential in the contestants they have seen so far and Spears admitted that she has yet to find a superstar.
"Potential... serious potential. But not quite X Factor," Spears told a show crew of this year's acts.
She added: "I feel like we've had... some bizarre performances overall... Pretty, pretty bad."
Fellow judge Reid chimed in by revealing that he "tends to agree" with Spears when evaluating contestants.
"She has amazing taste," Reid declared.
Spears retorted jokingly: "You ganged up on me one time, though... It wasn't nice."
Photo gallery - The X Factor USA judges at season two auditions:
Guest judge Walsh was teased by Lovato and Spears about his anonymity in the US prior to filling in for Cowell at the weekend, but the 'Womanizer' star later seriously said that she has actually always liked Walsh.
The X Factor USA returns to Fox this fall
Watch the trailer for the latest series of X Factor USA below: