Some fans left the Monday concert early and others said Diamond completed the concert without mentioning anything to the audience about his voice.
A statement from Diamond, the singer of such hits as "Sweet Caroline" and "Song Sung Blue," on Tuesday says a doctor has diagnosed acute laryngitis.
Diamond spokeswoman Eve Samuels says the singer is offering a refund to those who place a request before Sept. 5. "I haven't let you down before and I won't let you down now," the singer said in an apology on his Web site.
Another message says Wednesday's concert in Green Bay, Wis., will be rescheduled for Sept. 12, and Friday's concert in St. Louis, Mo., will instead take place Sept. 10.
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