Nelson, who has battled with a string of health complaints in recent months and years, was reportedly taken to a local hospital. Then, at 1am ET, Nelson assuaged his fans' worst fears with a tweet in which he said he was "feeling better" and blamed the altitude. "This is Willie," he wrote. "I am sorry to have to cut the SLC show short tonight. The altitude got to me I am feeling better now & headed for lower ground."
Billboard has reached out to his reps for further comment.
The latest health concern comes after a report published by Radar Online in March quoted an anonymous source saying Nelson was "deathly ill." Elaine Schock, Nelson's publicist, denied the claim and said he was "perfectly fine." Nelson nixed several shows in late January and early February with a "bad cold," though he has since returned to the road.
The Country Music Hall of Famer's most recent album God's Problem Child bowed atop Billboard's Top Country Albums chart in May, his 17th No. 1 on the survey (and third to arrive at the summit). God's Problem Child also cracked the top 10 on the Billboard 200 (peaking at No. 10).
Nelson has been the target of various online death hoaxes over the years. He addresses them in the God's Problem Child song "Still Not Dead."