It is understood the Finance Minister Brian Lenihan has been diagnosed with pancreatic cancer.
Initial tests are said to have shown that he is suffering with a malignant tumour.
The severity of his illness is to be assessed over the coming days.
Just before the Dáil broke up for their Christmas break the minister was rushed to hospital with a suspected hernia.
In a statement, the minister said he is "well and enjoying Christmas with his family and does not propose to talk to the media until the New Year".