Simon Cowell is thought to be lining up top singers as guest judges for The X Factor auditions.

Simon wants to draft in the likes of Robbie Williams, Ronan Keating, Paula Abdul and Mel B in a bid to boost ratings, according to The Mirror.

Dannii Minogue will not be at this year’s auditions as she is due to give birth in July and Simon hopes that getting big name stars involved will create a “extra buzz” around the show and attract even more viewers.

A source told the paper: “The stars would attend all the auditions days in one city each.

“It would create an extra buzz and make the initial shows even more exciting. Simon thought it worked well on American Idol, so it is something he is willing to try.”

Simon is said to be unsure if Dannii could mentor a group of singers is she’s not present at the auditions – but she denied on Twitter at the weekend that she had been axed.

The source added: “It is difficult to know if Dannii wants a big role until after she has her baby. The situation could be up in the air a while yet.”

Judges Louis Walsh and Cheryl Cole are said to be re-signing next month.