The 53-year-old singer said her doctor had asked her to rest her throat, reported Daily Mirror.
Boyle was told to avoid talking for 36 hours in a bid to let her sore throat heal and was forced to cancel her next gig in Santa Barbara next week.
"It's typical, I wake up on the first day of the tour and I have a sore throat. Still, us British carry on," she said.
She completed the sell-out show at the Balboa Theatre in San Diego, California , the first night of a massive world tour, but then was rushed to see a top throat specialist.