The mayor of Portland had expected to give singer a key to the city after her performance at Merrill Auditorium on Wednesday night.
But the arts organization Portland Ovations says Minnelli fell ill before her afternoon sound check and could not perform as scheduled. She was on her way back to New York City.
The 64-year-old was expected to sing her greatest hits and material from new CD, "Confessions," to kick off Portland Ovations' 80th season.
The Portland Press Herald says the organization is hoping to reschedule the concert and is requesting that ticket holders wait for further information.
Minnelli representative Scott Gorenstein says the singer isn't seriously ill and will resume performing in the next few days.