The 'Womanizer' singer is concerned her comeback tour, 'The Circus Starring Britney Spears' will flop after a large number of concert tickets remain unsold for the opening show in New Orleans tomorrow (03.03.09).

A source said: "Group sales are down considerably, and then you've got individual tickets that cost as much as $500 apiece. That's a lot of money to spend on an artist who isn't a sure bet right now."

The source added: "She's worked really, really hard to make this good.

Granted, there've been some hiccups along the way, but she's going to put on a good show. I just hope there are people there to see it. This is really her last chance."

Meanwhile, it has been reported the Pussycat Dolls - who are due to support Britney on the tour - have been caught up in a row over costs.

The girls apparently want to take their male back-up dancers on the road but have been told it will be too expensive.

In a leaked email between their record label head Jimmy Iovine and the band, he said: "We can't afford it. I'm sorry its hard enough right now with the album not selling that's why we did jai ho and re releasing the album. And we want to be able to keep the whole thing going at this level its not a choice its a reality."