The X Factor winner was due to launch her new album across the pond while supporting Christina Aguilera.
But just FOUR days after tickets went on sale, headliner Xtina pulled the plug saying she wanted to spend more time on the production. She has put the dates back - by a whole year!
A tour spokesman for Christina said: "She felt she needed more time to rehearse."
A source tells us: "This is a massive blow to Leona - cracking America was her next big thing this year.
"Simon has been keeping an eye on how she is launched in the States, so this is a disaster.
"Christina has said she has to promote her new album, Bionic, and her film debut, Burlesque. But it doesn't add up.
"She appears to be running scared from all the comparisons with Lady GaGa."
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