"I've always felt that the present arrangement with the euro would not stand the test of time in the sense that it would have to be modified," the Berkshire Hathaway chief told CNBC's "Squawk Box" in an interview that largely focused on his role in the Heinz-Kraft Foods merger.
On the euro, Buffett said, "You harmonized the currency without harmonizing a whole lot of other things that have big effects on the currency." He argued one can't work without other, "sort of like in the Civil War, saying we can't exist half-slave, half-free."
"The Greek situation may illustrate the kind of adjustments that are needed," Buffett added.
After talks with European leaders, including German Chancellor Angela Merkel, in the past week, the leftist government in Greece said it will present a package of reforms to its euro zone partners by Monday in the hope of unlocking aid and avoiding a messy default.
—Reuters contributed to this report.