Defence Minister Samuel Schmid is being treated in hospital for acute inflammation of the gall bladder.
A ministry statement said there were no complications, but that he would remain in hospital for 48 hours. He was admitted on Wednesday evening.
Schmid's appointments have been cancelled for Thursday and Friday. It is not clear whether he will be back at work next week. If not, his deputy, Finance Minister Hans-Rudolf Merz will stand in for him.
Merz himself returned to work on Monday after a six-week absence during which he had a multiple heart bypass.
Schmid has been under considerable pressure over the past few months over his handling of army affairs. His appointee as head of the armed forces was forced to resign in August in after being implicated in a case of sexual harassment.
He has also been criticised over two fatal accidents. In July 2007 six recruits died in an avalanche on the Jungfrau, and in June 2008 five were drowned in a rafting accident.
Despite the pressure, Schmid has resisted calls to step down.