Britney Spears is reportedly in a "desperate panic" about her upcoming residency.
The singer is due to take to the stage at Planet Hollywood Resort & Casino in Las Vegas on December 27, for the first in two years of shows.
Much has been made about whether she will lip sync, with the 31-year-old said to be terrified about whether her vocals will be up to scratch.
"She's in a desperate panic, because the pressure is on to prove she's still got it and the organisers are putting their foot down about no miming," an insider told British magazine Heat. "They know it's box office gold, because the whole world wants to see what Britney's voice is really like now."
The star has apparently completed intense vocal training as she battles to ensure she sounds as good as possible.
She released her last record Femme Fatale in 2011 and was slammed for many of the promotional performances she gave. Her dance moves were dubbed sluggish and it was deemed she had relied too heavily on backing vocals.
Now planning for her Las Vegas residency and promoting her new record Britney Jean, she is determined to show her doubters she is back to her best.
Workers at the resort have reportedly been told to reassure ticket holders the star will be singing live, while her manager has insisted this will be the case.
"No matter what anyone says, there's not a single artist who goes out there and does full choreography and is singing without a vocal track underneath them at the same time," he added. "It's physically impossible."