He was admitted to an area hospital Tuesday for an abdominal illness and is canceling his weekend shows in Clarksville, Tenn., and Berea, Ohio.
Otto says in a statement that he has "been feeling badly on and off for a while now but didn't think it was serious."
He adds that he "may have been a bit distracted by all the excitement of baby Ava's arrival." His wife, Amy, gave birth to a healthy baby girl on Aug. 24.
Otto says he will be down for a few days but hopes to be back in action soon.
Otto scored his first No. 1 hit in 2008 with "Just Got Started Loving You." He also co-wrote last year's CMA song of the year, "In Color," sung by Jamey Johnson. Otto is releasing a new album Sept. 14.