The head of Greece's co-ruling Socialist PASOK party, Evangelos Venizelos, was taken to hospital overnight complaining of stomach pain but is expected to be discharged on Tuesday, his doctor said.
"It is related to gastroenterological disorders. He checked into our hospital for precautionary reasons," the head of the Hippocratio Hospital's cardiology unit, Christodoulos Stefanidis, told Greece's Skai TV.
"Based on the information so far, he will be discharged today."
Venizelos is foreign minister and deputy prime minister in Prime Minister Antonis Samaras's coalition government.
Samaras announced a sweeping cabinet reshuffle on Monday aimed at showing Greeks he has heeded their call for change after his co-ruling center-right New Democracy party trailed the leftist opposition SYRIZA in European elections last month.
Economist Gikas Hardouvelis was named finance minister, signalling the government's intention to keep up a difficult reform drive demanded by Greece's international lenders.
The cabinet is due to be sworn in later on Tuesday.