Miguel Galan, the president of Spain’s National Centre for Football Coaches (CENAFE), has accused Tebas of sharing confidential financial data relating to Barcelona with Athletic.
Williams, 22, looked set to join Barcelona before changing his mind at the last minute after the club were unable to offer his guarantees he would be registered without issue.
Galan wrote on X: "Meeting of @AthleticClub with @Tebasjavier revealing confidential information about @FCBarcelona_es. Today I was able to learn what was said in the famous meeting between @Tebasjavier and @AthleticClub.
"At said meeting, the president of @AthleticClub was shown the information from FC Barcelona's interim financial statements, allowing him to verify on-site that the profit and loss statement did not reflect any amount related to the corporate operation of selling VIP seats.
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“Furthermore, the president of LaLiga explicitly reported on the reduction of FC Barcelona's LCPD and that it had neither the balance nor the capacity for registration, in compliance with financial fair play. Finally, he also presented the limited review report signed by Crowe Auditores España SL.
"According to the confidential information that was revealed to Athletic Club de Bilbao, a situation arose in which Nico Williams requested an additional guarantee in the form of a release clause.
“FC Barcelona, acting with good judgment, was not willing to accept said condition. Consequently, the non-signing of Nico Williams is attributed solely to the distrust generated by the president of LaLiga toward the player's agent, as well as toward the player himself and his family.
"Following the meeting between the president of LaLiga and the president of Athletic Club de Bilbao, confidential financial information about FC Barcelona was provided to Nico Williams, which was exaggerated in order to generate concern in the player's family and attempt to convince them to include a release clause that lacked any logic."