PIC: Gaunt LeAnn Rimes Sings National Anthem

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LeAnn Rimes proved why she's a Grammy-winning, multi-platinum selling singer in Houston, Tex. on Monday, delivering a soaring rendition of the National Anthem for basketball fans at an NCAA championship game.

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But the singer, 28, displayed more than just talent and patriotism: Wearing a form-fitting, white lace Dolce & Gabbana dress that accentuated her gaunt, rail-thin frame, Rimes didn't dispel continuing concerns about her weight loss. See more scary photos of LeAnn at the NCAA game.

Indeed, those in her inner circle are worried, sources recently told Us Weekly. "LeAnn's pals are telling her not to lose any more weight," an insider said.

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And although Rimes has insisted via Twitter "I am a healthy weight," her friends say the stress of her upcoming wedding to Eddie Cibrian — and more, are behind her shrinking figure.

Cibrian, 37, who cheated on wife Brandi Glanville with Rimes, recently hit Chicago to film his new series Playboy. "Eddie's…filming with all these beautiful women," the source says. "It's the stress of not being able to trust him."

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And Rimes has said in the past that her devotion to the gym has helped her deal with a chaotic personal life, the insider notes she's "now addicted" to working out.

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