Athletic Bilbao President Josu Urrutia says he does not understand how someone within the club would continue to damage it by leaking recordings of private dressing-room conversations.
• Bielsa plays down Llorente row
A partial recording of manager Marcelo Bielsa's talk to his players, the day after May's Copa del Rey final defeat to Barcelona, was leaked to the Basque media last week, while a fuller version found its way into the papers on Wednesday.
The Argentine is heard to give a damning verdict on the side's poor end to the season as well individual performances, during both the Barcelona loss and the earlier defeat to Atletico Madrid in the Europa League final.
He goes on to tell his players that they have disappointed the club's fans and are "premature millionaires".
The coach does however take responsibility for what happened and tell his players that they are young and will have more opportunities in the future.
Most worryingly for Athletic, Urrutia had revealed that a member of the squad had for some reason now decided to try and damage their club - something which he finds very disappointing.
"It is a disappointment, something lamentable," he said. "It was a private setting with just the coach and 25 players. I do not understand the recording, nor the leaking."
The former Athletic midfielder, who claims he has not listened to the tape or read the transcript, said rumours that they had been deliberately leaked by the club in order to destabilise Bielsa's position were untrue.
But he does concede there must be a specific reason as to why the tapes have been leaked.
"Someone must have a reason to leak them, but it is not coming from inside," he said. "I do not understand how anyone can say the club would leak something like this. It is totally false and comes close to slander."
The leaking of the tapes is the latest problem to hit the Basque club in recent months. In July Bielsa rowed with construction workers at the training ground after a disagreement over the progress of renovations. While in August key player Javi Martinez left for Bayern Munich after a long transfer saga and was then accused of breaking into his old dressing room to retrieve his belongings.
And just last week centre-forward Fernando Llorente, who has been benched after refusing to sign a new contract, had a public argument with Bielsa at training.
Some of the gloom was lifted by Sunday's 1-0 win over local rivals Osasuna, but the club still sit 16th in the table, with just two wins from eight La Liga games.
All this has led to some heavy criticism of the current President and coach from fans, pundits and former players in Bilbao.
Urrutia admits that this has not been a good period for the club, but wants everyone concerned with its wellbeing to now pull together.
"We are all responsible for Athletic, someone can make a mistake, but he should be working for the good of the club," he said. "I am a member, ex-player and now president. When I was outside, I tried to be supportive, not just to talk, but to act. I am not saying that I cannot be wrong sometimes, but in the future Athletic can count on me."