The 82-year-old singer's team announced he would reschedule or cancel the first three dates of his Django and Jimmie tour with the 78-year-old musician Wednesday on Facebook.
"Unfortunately Willie has been feeling under the weather so a couple dates have been rescheduled and one canceled. Sorry for the inconvenience.
10/15 Florence, SC is rescheduled to 4/6/16 10/16 Roanoke, VA is rescheduled to 10/19 10/17 Reading, PA has been canceled."
"This is all news to us at the moment and we're still getting details on Willie's medical condition," Florence Civic Center senior marketing manager Nick Hooker told Taste of Country. "We've been told this is not life-threatening, but will require several weeks to fully recover."
Nelson's younger son by Annie D'Angelo, Lukas Nelson, later reassured fans about his father's condition in a Facebook post, writing, "Thanks for the prayers and love for dad, his health issue is minor and he's doing great, love to all."
Nelson and Haggard are expected to play Oct. 21 in Bloomington, Ind., and will bring the tour to a close Nov. 28 in Fort Worth, Texas. The former last released the archival album Willie's Stash, Vol. 1: December Day in December, while Haggard debuted Working in Tennessee in October 2011.