Simon Cowell believes ''real chemistry'' is more important than attracting celebrity judges for 'X Factor' USA.

The music mogul is currently recruiting two new mentors to the panel of his pop star search show after Britney Spears and L.A. Reid quit but he isn't looking for star power.

A source told the New York Daily News: ''Simon delivered a simple message: Forget the big names and go for chemistry. He said all these shows have become distracted by signing celebrities rather than judges who really have something to say. We have all seen that big names don't translate into big ratings.

''Chemistry is top of the list of demands for next season. [Only Demi Lovato will return because her chemistry with Simon was] the best thing about the panel last year.''

It was recently claimed Jennifer Love-Hewitt is in the running to be a judge on 'X Factor' USA.

The 34-year-old actress - who hit the charts in 2002 with her single 'BareNaked' - is reported to be joining Simon and Demi on the third season with a source saying: ''Simon is very interested [in Jennifer].''

Jennifer has released four albums in her career but turned her back on music in 2004. However, this year she recorded a cover of 'I'm a Woman' to promote the second season of her TV show 'The Client List'.

Kelly Rowland has also been tipped to take on a role on the panel.

A source said previously: ''Simon has always remained a fan of Kelly's and she's most definitely in the mix to join the judging panel on 'X Factor' USA.''

Mario Lopez will be returning to the screens as a presenter on 'The X Factor', but Khloe Kardashian has not had her contract renewed.

Producers said in a statement: ''Khloe Kardashian will not be returning to co-host 'The X Factor'. We really enjoyed working with her and wish her all the best in the future.''