El Youssoufi on Sunday was admitted to intensive care unit at the Sheikh Khalifah hospital in Casablanca following a health problem, the agency added.
Born in Tangier on March 8, 1924, El Youssoufi served as Prime Minister of Morocco from February 1998 to October 2002.
As a human rights lawyer, he was exiled in France for 15 years before returning to Morocco in 1980.
In 1992, he became the new leader of the Socialist Union of Popular Forces, the major opposition political party in Morocco at that time.
He retired from politics in 2003