Van Zant, 46, came out of surgery at Stanford University Medical Center in Palo Alto, Calif., around 10 p.m., said manager Ross Schilling. His condition was not immediately available.
"He had been feeling bad the past couple of days," Schilling told The Associated Press. "He had performances Tuesday and Wednesday and sucked it up last night as far as performing with some pain."
On Thursday morning the singer went to see a doctor, who determined through an ultrasound that the appendix was severely inflamed and emergency surgery was needed, Schilling said.
Van Zant is expected to need at least a week to recover, forcing the cancellation of three shows: Shoreline Amphitheater in Mountain View, Calif., on Friday; the U.S. Marine Corps base at Twentynine Palms, Calif., on Saturday; and Sunset Station Casino, Henderson, Nev., on Sunday.
He also won't attend Tuesday's Academy of Country Music awards, where he and his brother, Donnie, are nominated for duo of the year for their work performing as "Van Zant."
Their brother Ronnie Van Zant was a founding member of the Southern rock group best known for songs like "Sweet Home Alabama" and "Free Bird."
Ronnie Van Zant, Steve Gaines and backup singer Cassie Gaines were killed in a plane crash in Mississippi in 1977. The group was inducted into the Rock and Roll Hall of Fame in March.