John Mayer has been hospitalised for an emergency appendectomy.
A representative for the Grammy-winning musician said Mayer was admitted to the hospital Tuesday morning.
He had been due to perform at a concert in New Orleans with the Dead & Company, but that date has been postponed.
Tickets for that show can be used for a rescheduled date or refunded.
The 40-year-old had performed with the Dead & Company as recently as Sunday.