Fans with tickets to see Willie Nelson and Alison Krauss together in concert next month will be disappointed. The pair have announced that Krauss has had to cancel or reschedule several shows because of health problems.

“Due to an unforeseen and urgent health concern that requires immediate attention, we have been forced to reschedule and unfortunately cancel a few select shows on the upcoming tour with Willie Nelson," reads a post on her website. "A list of the affected shows, along with makeup dates and ticket refund/exchange policies are listed below. We sincerely apologize for any inconvenience.”

While the announcement does not clarify the nature of Krauss' physical concern, she has previously canceled shows due to a vocal condition called dysphonia, which can result in a hoarse or rough voice, dryness of the throat, and the inability to sing in the upper range. It is unclear if this is the cause for the cancellations.

Krauss' publicist tells that the singer needed to undergo a "minor medical procedure" that requires a few days of recovery, and needed to be taken care of before the tour began.

Krauss and Nelson were supposed to kick off their co-headlining tour on May 1. Their tour was scheduled to run through July.

A list of the affected shows is posted below. Refund and exchange information is available here.

5/1 - Murray, Ky. – CFSB Center – Rescheduled
5/2 – Atlanta, Ga. – Chastain Park Amphitheatre – Rescheduled
5/3 – Knoxville, Tn. – Thompson-Boling Arena – Rescheduled
5/4 – Cary, N.C. – Koka Booth Amphitheatre – Rescheduled
5/6 – St. Augustine, Fla. – St. Augustine Amphitheatre – Rescheduled
5/17 – Birmingham, Ala. – BJCC – Canceled
5/18 – Augusta, Ga. – James Brown Arena – Canceled