McPhee, who joined the tour on July 28 after missing the first few weeks because her doctor ordered her not to talk or sing, tripped backstage before a show at the Bobcats Arena in Charlotte, N.C., the paper said.
The 22-year-old trooper went on with her set anyway, according to the Post, singing two songs with slippers on. She was later taken to a hospital for X-rays which showed a hairline fracture.
"She's in discomfort, but she's fine," a rep told the Post. "She will continue on the tour and is not defaulting."
When the California native failed to join the tour on time a few weeks ago rumors swirled that the singer thought she was too good for "Idol" or that she'd had a bulimia relapse. She denied both.
In June, McPhee signed a record deal with music mogul Clive Davis in conjunction with 19 Recordings Unlimited.
By Amy Bonawitz