Badie Arif Ezzat told the Al-Hayat Arab newspaper on Thursday that Tareq Aziz, one of the most recognisable figures from Saddam Hussein's deposed regime, is "in agony and I do not expect him to live more than a month" following the cerebral embolism and heart problems.
A cerebral embolism occurs when a blood clot creates a blockage in an artery in the brain and is a common cause of a stroke.
Ezzat did not say when Aziz, 69, had been struck by the illnesses but noted that the deterioration was apparent when he visited several of his clients to mark the Muslim Eid Al-Adha festival which started on Tuesday.
Aziz, the top Christian in Saddam Hussein's regime and a fluent English speaker, became one of its best-known figures for his frequent tirades against the West as foreign minister.
Appointed foreign minister in 1983 and then deputy prime minister in 1991, Aziz was largely believed to have wielded little real power of decision-making.
But Saddam was said to listen to the widely-travelled, avuncular figure.
Previously omnipresent in the media with his trademark thick glasses and military uniform, Aziz maintained a mysteriously low profile in the build-up to the US invasion of Iraq in 2003 that ousted Saddam's regime.
Aziz turned himself over to US forces in April 2003 and has been questioned several times by judges of the Iraqi special tribunal trying Saddam and top aides for crimes against humanity and war crimes.
Ezzat said Aziz was now being held by US forces in a room "reserved for dogs" that measures just two metres long and a metre wide which he is only allowed to leave for brief periods.
The lawyer's latest remarks contrasted with comments made to AFP in December when he said Aziz was in relatively robust health even though he had lost a lot of weight.
Aziz has been accused of two counts of mass murder, allegedly committed in 1979 and 1991, and punishable by death if found guilty.
He denies the charges and Ezzat said the accusations had now been dropped owing to lack of truth but a new case had been brought against Aziz for alleged embezzlement of public funds.