Bashar al-Assad's uncle, the 'Butcher of Hama', hospitalised while standing trial for fraud in France
"He has been in intensive care since last night [Monday]" at the American Hospital in Neuilly-sur-Seine west of Paris, Siwar al-Assad said.
Rifaat al-Assad suffered from a form of internal bleeding "and is not very well". He will need to stay in intensive care for two or three days.
The younger brother of the late Syrian dictator Hafez al-Assad - father of the current dictator Bashar Al-Assad - is standing trial in Paris for crimes allegedly committed between 1984 and 2016, including aggravated tax fraud and misappropriation of Syrian funds.
The charges relate to his vast property empire in France.
France's national finance prosecutor called Monday for a four-year prison sentence and a 10-million-euro ($11.1 million) fine.
The prosecutor also called for the confiscation of all his real estate, valued at 90 million euros ($99.5 million).
Rifaat al-Assad, who divides his time between France and Britain, denies the charges.
The 82-year-old, dubbed the "Butcher of Hama" for commanding troops who put down an uprising in the central Syrian city of Hama in 1982, has been under investigation in France since 2014.
An estimated 20,000 people were killed in the massacre in Hama which followed the uprising, according to human rights groups.
Rifaat has also been linked to the 1980 killings of hundreds of prisoners as well as Syrian army abuses in Lebanon in the 1970s and early 1980s.
Formerly Syria's vice president, Assad left his home country in 1984 after mounting a failed coup against his brother Hafez, who ruled Syria with an iron fist from 1971 to 2000.
After he arrived in Europe, Rifaat al-Assad's lavish lifestyle, four wives and 16 children soon raised eyebrows.
His reported French fortune includes two Paris town houses, one measuring 3,000 square metres (32,000 square feet), as well as a stud farm, a chateau and 7,300 square metres of office space in Lyon.
He and his family also built up a huge portfolio of 507 properties in Spain, valued at around 695 million euros, Spanish legal documents show. All his properties in that country were seized by the authorities in 2017.
Assad has maintained that his lifestyle was made possible by gifts from the Saudi royal family amounting to more than a million dollars per month.
But while his lawyers claimed to document gifts of almost $25 million between 1984 and 2010, French investigators registered transfers from Saudi Arabia totalling only $10 million.
Assad's trial opened on 9 December.
This is only the second trial of a foreign dignitary in France on charges related to "ill-gotten gains".
In the first, Equatorial Guinea vice-President Teodorin Obiang received a three-year suspended jail term in October 2017 after being convicted of using public money to fund a jet-set lifestyle in Paris.