Us Weekly reported that the official reason for McPhee's absence is that she has been suffering from bronchitis and laryngitis. However, the magazine said, public sightings of the singer have caused many to doubt that.
The 22-year-old "Idol" runner-up was reportedly seen swimming days before she postponed her tour due to her illness -- and even attended a public photo shoot the day after the tour began.
One source has alleged that McPhee's absence from the tour is directly due to her publicized eating disorder, which a representative for the singer has denied.
McPhee, who was set to join the tour Thursday, said the speculation has been difficult for her, TMZ.com reported.
"It was definitely difficult, especially with the media making assumptions about what exactly it was -- she's ditching the tour for a movie, all these silly things," she said. "It's just part of the business and I'm happy I'm healthy."