AUSTRALIAN Idol judge Mark Holden has described Matt Corby as the biggest potential star the show has produced but, for now, has thrown his support behind Natalie Gauci.

Disappointed by what he calls Corby's "spoilt child" attitude, Holden has pulled a shock about-face on the 17-year-old favourite who he has backed from the start of the season.

Holden says it was Corby's handling of the winner's single controversy, as well as some recent lacklustre performances, that prompted him to switch to Gauci, who is also firming with betting agencies.

Corby was quoted last week as saying he wasn't fond of the single penned for the winner by Sony, titled Here I Am, but later backpeddled on the issue and called it a "great pop song".

Corby or Gauci will be crowned this year's Australian Idol at the Opera House grand final tomorrow.

"Matt had an opportunity to define himself and put Sony on notice by saying 'I am a 17-year-old Generation Y kid and I don't necessarily accept what you Baby-Boomers are giving me here'," Holden said.

"But I think he missed that opportunity and he took the approach of a beauty pageant contestant. And the most disappointing thing is that when he sang the song (on air) it showed that he wasn't into it and that is a spoilt child thing.

"At that point you be honest and say 'This is not a song I would choose but I'm going to give it 200 per cent anyway'.

"At that point I switched to the Natalie camp."

Holden isn't the only one. Punters are deserting Corby in droves while his rival's odds of victory have slimmed from $3 to $2.40 with betting agency Lasseters.

But according to Holden, it won't affect Corby's earning capacity.

The singer-songwriter has the potential to be the most successful Idol contestant in the history of the Channel Ten talent quest and, Holden says, is the only contestant with genuine international appeal.

"He's got the world at his feet, no doubt about it," Holden said. "But my advice to him right now would be to take the Missy Higgins approach and take a year off to go backpacking or something. Go and work in an indigenous community or do something to help your personal development.

"He's got all the time in the world."