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.
Turkey has found itself in a circle of countries subject to US and European sanctions. Are they dangerous for Ankara? What is Turkey going to do in response?