Citing "personal reasons," Fuentes left with the Basque club in danger of its first relegation from Spain's top league in 40 years. Real Sociedad is 18th with 33 points, four from Athletic Bilbao and safety.
Later Friday, the club's board will name a temporary replacement until a new president is elected by members on June 30.
Russian Foreign Minister Sergei Lavrov said at a briefing in Beijing that the question about the shipment of S-300 anti-aircraft missile systems to Syria had not been resolved yet. However, Syrian Ambassador to Russia Riyad Haddad said that S-300 missile systems had been delivered to Syria last month