 Having finished his football grooming with Real Sociedad, he was the top scorer (across all four groups) in the third division with the B-team in the 2005–06 season, and also made his La Liga debut on 12 February 2006 in a 0–1 away loss against Atlético Madrid.In 2007–08, he scored 16 second level goals as the main squad finished fourth, falling short of a return to the top flight.On 8 November 2008, Díaz de Cerio suffered a serious injury after a collision with SD Eibar player Zigor, fracturing the tibia and the fibula of his right leg.