The "American Idol" runner-up tripped backstage before a performance Tuesday night in Charlotte, N.C., said Roger Widynowski, a representative for McPhee's record label, RCA.
However, McPhee was able to take the stage — wearing "slipper-sandals" — to sing two songs. She went to a hospital after the performance, and X-rays showed a hairline fracture in her left foot, Widynowski told The Associated Press on Thursday.
Widynowski said McPhee is in "good" condition and will stay on the tour.
The 22-year-old singer missed the first few weeks of the tour because her doctor told her not to sing. She joined the tour in Washington on Friday.
McPhee, known for her sultry looks and her cover of "Somewhere Over the Rainbow," lost the most recent round of the FOX talent competition to Taylor Hicks.