Willie Nelson has been forced to pull out of the opening dates of his joint headline US tour with Bob Dylan on medical grounds.The 91-year-old was due to kick off the ‘Outlaw Music Festival Tour’ alongside Dylan yesterday (June 21) in Atlanta, followed by Charlotte and Raleigh, but he will now miss all three dates.“We regret to inform you that Willie Nelson is not feeling well and, per doctor’s orders, has been advised to rest for the next four days,” read a statement on social media. “He is expected to make a quick recovery and join the Outlaw Music Festival tour next week.”“In the meantime, Lukas Nelson and the Family Band, along with a few guests, will perform a special set to include Willie’s classics and other songs.”The tour was announced in February, a run of 26 dates around North America that is set to last until September.