Mariah Carey reportedly pulled out of her Las Vegas show on Wednesday (13.05.15) because she was unprepared.

While the 'We Belong Together' hitmaker has claimed she was forced to miss her '#1 to Infinity' show at The Colosseum at the Caesars Palace Las Vegas Hotel and Casino because she was diagnosed with bronchitis, insiders have claimed she simply hadn't rehearsed enough.

A source close to the star - who is just one week into her Las Vegas residency - told the New York Daily News newspaper's Confidenti@l column: ''Mariah simply didn't rehearse enough before starting this many concerts and now she's feeling it.

''Leading up to the first show, everyone involved was wondering why this wasn't rehearsed to death.''

The source added that the 45-year-old singer wasn't pleased with her performance in her first shows and had been criticised over her timing on stage.

They explained: ''She can sing, but she hardly walks during the show. They're always wheeling her out on some prop.''

Mariah broke the news she was suffering with the respiratory illness and had been told by doctors to rest in an Instagram post.

She wrote: ''Hey guys ... I've been fighting bronchitis for the past few days.. almost better but on mandatory vocal rest per doctor's orders. I'm so sorry to cancel tonight's show but I promise to make it up to you!!! Love you always, MC (sic)''

Ticket holders took to social media shortly afterwards to express their disappointment and frustration.

One disheartened fan posted: ''The least she could have done was to sit down and do a meet and greet with every person that attended the show ... Taken a selfie with them, and give them a signed free poster. People would have at least been happy to meet ''The'' Mariah Carey. Instead we got a flyer saying that the show would've be rescheduled. Meanwhile our trip cost like $1000 not even including our tickets. They better attend to this soon, and give us 2/3 night stays at the Caesar's for free, along with free tickets to the show (with the same seats we paid for) ... Cause if they don't attend to this, the media is going to eat her up. (sic)''

Mariah's next scheduled concert is due to take place on Saturday (05.16.15).