"To my fans, I’m sorry to cancel my tour, but I have a breathing problem that I need to have my doctor check out," he wrote. "I’ll be back Love, Willie."
Fans of the "On the Road Again" singer responded with words of kindness, asking him to take care of himself and to get better soon.
"Get well soon and you take it easy. It's not worth your health for a tour. You take care of you first," one Twitter user wrote.
Another said: "Even legends need to take a break sometimes. Take care of yourself. We’ll wait."
Prior to his announcement, Nelson had just finished performing in Toledo, Ohio, and was scheduled to appear Friday in Grand Rapids, Mich.
In September, he was scheduled to perform at the Farm Aid concert with John Mellencamp, Dave Matthews, Neil Young and Bonnie Raitt, before wrapping up his tour in Thackerville, Okla., in November.
The tour cancelation isn't Nelson's first due to illness. He canceled an appearance at the Outlaw Music Festival last summer due to illness, and was forced to cancel several dates in 2018, too.
The Associated Press contributed to this report.