(Cover) - EN Showbiz - Simon Cowell is reportedly concerned that his hiring of Britney Spears on The X Factor was a blunder.

The pop songstress recently joined the coveted judging panel of the TV talent show on a multimillion dollar contract. She holds post alongside Demi Lovato and returning stars Simon and L.A. Reid.

Britney sparked controversy for walking off set on her first day on the job last week, leaving an empty judging seat for over four contestant performances.

Although it is rumoured that Simon sanctioned such break allowances in Britney's original deal, it is now said that the producer and music mogul regrets his decision.

"He wonders if hiring her was a mistake," a source told Us Weekly magazine.

Simon, who is infamous for his brusque critiques, is also apparently dismayed with Britney's kind judging approach.

"[Britney] always said nice things, even telling one mediocre singer he could be 'bigger than Justin Bieber.' Simon was shocked!" the insider revealed.

Simon is considering how Britney will fare on the air later in the season.

"I don't know how she's going to handle the live shows!" the source said. (C) Cover Media