The European Union's executive said in a statement that the 64-year-old Juncker "will undergo an urgent cholecystectomy," referring to the surgical removal of the gallbladder.
Juncker had been on vacation in Austria. He is in the final months of his five-year term as European Commission president, one of the leading jobs in the 28-nation EU.
He had been scheduled to go to the Group of Seven meeting in Biarritz, France, next week. Juncker had been troubled by a bad back over the past years.
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