Oyarzabal, 21, is among a group of players who have been picked by Spain boss Julen Lopetegui to boost the numbers in the squad due to the absences of those that represent Real Madrid.
Despite not being included in the World Cup squad, Oyarzabal is "proud" to be given the opportunity to be a part of the nation's build-up for this summer's tournament in Russia.
"I'm proud to help the team prepare for the World Cup in the best way possible and it will be very good to train with the players I'll be with," Oyarzabal told Sociedad's official website.
"The holidays will be a little shorter but I don't care if it is for this reason. I'm happy with the season I had and thought I played well. When you have confidence and the support of your teammates you try harder and things go easier for you."
Oyarzabal made his international debut for Spain back in May 2016.