12/18/2007 at 12:45 PM EST
Ashley Tisdale apologized to fans for missing shows in Miami and Philadelphia last weekend because of her recent rhinoplasty procedure
"When my surgery was scheduled, we didn't think it would be necessary to cancel the shows because my doctor thought I would heal in time," she writes on her Web site.
"Unfortunately, the deviated septum was more significant than we originally thought so the healing process is taking longer."
The High School Musical
star still flew to her gigs with the crew and dancers, hoping she would be well enough to make it onstage, but then "had to make the difficult decision to cancel the appearances," she says.
Tisdale, 22, also didn't perform at the Z-100 Jingle Ball in New York on Friday, although she put in an appearance and signed autographs for fans.