Simon Cowell warned Cheryl Cole to "raise her game" days before she was sacked from 'The X Factor'.

The British singer was sensationally dismissed from the judging panel of the TV talent contest after just four auditions, but the music mogul - who had previously worked with Cheryl on the British version of the show - had advised her to be more vocal towards the contestants.

Recalling a phone call he made to her after the second day of auditions, Simon explained: "I said: 'Cheryl, you've got to raise your game a bit. This is America, it's a much tougher market.'"

Simon felt Cheryl was uncomfortable on the US panel because she wasn't as well known as she is in the UK and believes the muted reception she received caused her to become withdrawn.

He told the Hollywood Reporter: "I came to the conclusion that she may not be as comfortable here because I was seeing a different person.

"She was like Princess Diana when she would walk out in England, and I accepted the fact that people didn't know her here, but I think it did have an effect on her."

Simon and Cheryl then began negotiations for her to return to the UK show, with her reportedly agreeing to a huge pay rise.

Simon said: "We had gotten to the point where she wanted my dressing room."

However, the 'Promise This' hitmaker never agreed a final offer and hasn't spoken to her friend since.

Cheryl has since been replaced on the panel by Nicole Scherzinger, who joins Simon, L.A. Reid and Paula Abdul on the US show, which is due to launch in the coming weeks.