X Factor supremo Simon Cowell says he wants to decide on the show's judging panel this week and has "a shortlist" of likely contenders for the job.
Veteran Louis Walsh has been axed from the show - freeing up one space on the panel - and the future of fellow judges Mel B and Cheryl Fernandez-Versini has not been confirmed.
Cowell refused to rule out a return to the hit show for former star Tulisa Contostavlos, but laughed off suggestions Britain's Got Talent (BGT) judge David Walliams could join the panel.
He said Walliams would be a " terrible fourth judge. I can confirm that would never never happen".
Cowell, who at a charity night in central London for Together For Short Lives which helps terminally ill children, said he had not made a final "decision" on the X Factor panel and added: " I'd like to get it done this week if I can."
The music mogul said he looked for enthusiasm in a judge, saying : "I have seen people go onto these shows for a year and they've got zero interest in the artists and they want to sell a few concert tickets, sell a few records and a book then disappear."
Cowell also said he was planning to change the show's "overall format" and would bring in "more" six chair challenges - the section of the show introduced two years ago which allows the panel to swap contestants in and out before deciding who goes to the judges' houses stage.
He also hinted at plans for next year's BGT which marks the show's 10th anniversary, saying: "W e were thinking actually, although I don't know if the contestants would do it, that maybe before the normal final we would get all the p ast winners of Got Talent to compete in one competition. We'll have the best of the best."