Ajax have revealed the on-field treatment received by Abdelhak Nouri after he collapsed during a game was "inadequate" and could have worsened his condition.
Nouri was left with permanent brain damage after experiencing heart failure during Ajax's friendly against Werder Bremen in July 2017.
Ajax initially suggested Nouri was given all the correct care, but managing director Edwin van der Sar has now accepted the club should have handled the situation better.
"We have important news about the terrible incident concerning Abdelhak Nouri last year," Van der Sar said in a lengthy statement to the media on Monday. "Based on new insights, which we, unfortunately, did not discover until very recently, we have reached new conclusions.
"These are that the treatment received by Abdelhak Nouri on the field in Austria in July 2017 was inadequate. We recognise our responsibility and liability for the consequences of this.
"First of all, I would like to offer the Nouri family our apologies for the fact that it took us so long to change our point of view on this matter."
After new information came to light, Ajax consulted cardiologists who agreed "attendants were insufficiently focused on measuring the heartbeat, circulation, and a potential reanimation".
Furthermore, the defibrillator that was available to those treating Nouri should have been used earlier to clarify the situation.
"After clearing the air passages, the attendants should have taken a moment to reflect, as the situation was not improving," Van der Sar continued.
"Allow me to say this: if there is anyone who, at that moment, wanted to give Appie adequate help, it was the two attendants who were taking care of him.
"The cardiologists also found it unlikely that, after Abdelhak had collapsed, an effective blood circulation was taking place. Had the defibrillator been used, this would have become apparent, and then reanimation could have begun at that point.
"Had this happened, it's possible that Abdelhak would have come out in a better condition. This isn't certain, but it's a possibility."
Van der Sar said the new developments have come as a "an enormous shock" to Ajax, with the club apologising to Nouri's family and pledging further support to them.
"The first thing that we will be doing is entering discussions again with the Nouri family," the managing director said. "We now need to do what’s necessary in order to fulfil the responsibility we have as a club, but also as human beings, colleagues and friends of 'Appie'.
"We wish to resolve this in a good way and this is what we are focused on. The mandate of the arbitration was to determine whether or not we had provided adequate treatment on the field. We did not, and we therefore assume responsibility for this.
"We have also committed to the family, previously, that if it turned out that we were in the wrong, we would take responsibility for it. We first need to discuss with the family what arrangement this will lead to.
"I would like once again, in front of you all, and on behalf of Ajax, to offer our deep apologies to Abdelhak, his family and loved ones. It must have been very frustrating that for a long time our conclusions were different, on top of the sorrow of what had happened to Abdelhak."