Real Sociedad sold the midfielder to Arsenal over the summer for €55m.
And Zubimendi's former youth club Antiguoko is taking the case to court, insisting they are owed €1m from the deal.
Roberto Montiel, technical Director of Antiguoko, said: “Currently, the relationship with Real Sociedad is very bad on their part.
“We had an agreement with Real Sociedad until 2020. Since then, we have an agreement with Athletic Bilbao.
“When Zubi signed for Real Sociedad, it was agreed that, in the event of a transfer, we would receive 5 per cent up to one million euros in return.
“With this behavior, we decided not to renew the agreement with them because we felt mistreated by them.”
Antiguoko also said: “They are obsessed with crushing us at all levels. They want us to be more and more inferior.
“The Provincial Council of Guipúzcoa has put in place a law that is subject to Real Sociedad of ‘territoriality’.
"This means that a boy or girl from a town bordering 5 kilometers from San Sebastián up to under-14 category cannot sign for Antiguoko.
“In other words, any boy or girl within the entire periphery of San Sebastián and its surroundings cannot sign with us, even though the kids’ parents wanted them to join us."
Madness!
Montiel also said, “This would be translated as explaining that a child from a neighbourhood on the outskirts of London cannot sign for any club in London up to under-14 category. Madness!
“Real Sociedad collected the transfer fee from the sale of Martín Zubimendi from Arsenal and has not paid us the five per cent that corresponds to us according to the agreement.
“Real Sociedad has not said anything, and we have made the request in court. And we will have an administrative dispute to reach an agreement.
“They will maintain their position of not paying us. That money is very important to us because we invest it in our academy.
“Another example of the poor relationship with Real Sociedad is last season. We were holding an official event to reward Martín for all the sporting achievements he has achieved, and Real Sociedad did not give him authorisation to collect the award. As a result of that decision, we had to cancel the event.
“We have already agreed with Martín that we will hold the event at the end of this season. Furthermore, I don’t think a former Antiguoko player, Mikel Arteta, will pose any problem.”