The Spain winger was expected to sign for Barca this summer, but instead rejected their offer and chose to stay with Athletic Bilbao and sign a new contract. Nico did the same a year ago after the Euros.
Laporta, after signing Marcus Rashford on-loan from Manchester United, revealed: "The signing of Luis Díaz (Liverpool) was complicated and we were in the middle of negotiations with Rashford, but Nico Williams' agent came to us offering the possibility of signing him.
"(Barca sports director) Deco told me that we had to listen to the proposal from Nico Williams' agent. My priority, in principle, was Luis Díaz or Rashford. In these cases, I always trust the sporting directors, who told me that we had to listen to what he was proposing.
"There was a big difference between what we were told and what actually happened in terms of payment terms, the agent's commission... a whole series of variables that indicated the deal wouldn't happen."
He added, "Deco set a 48-hour deadline because if they didn't accept our terms, we wouldn't go through with the deal, and ultimately, the deal fell through."