Haggard, 74, entered the Macon hospital on Tuesday night after he cancelled a show in that Georgia city seven minutes before he was to take the stage because he was too ill to perform, said Frank Mull, his tour manager and close friend.
A member of the Country Music Hall of Fame, Haggard is best known for songs including Mama Tried, Okie from Muskogee and The Fightin' Side of Me.
Haggard had been scheduled to perform again on Wednesday night in Columbus, Georgia, but that show and the rest of the January slate will be rescheduled for April, according to Haggard's Los Angeles-based publicist Tresa Redburn. Haggard will take time off to recover and resume his tour in February, Redburn said. Haggard lives in Northern California.