Betis were stunned 2-1 after Giovani Lo Celso had given the visitors the lead.
Afterwards, Adrian slammed the performance: "The first thing is to apologise to the fans because, honestly, it was a real joke. I saw it from behind and, for me, the game we played was shameful.
"You can't imagine a game like that. It's not just in the Conference, it was the same in the last game in Valencia . In four minutes we were turned around by an opponent that, a priori, should be smaller than us. We make them great, we give life to anyone. What I said, I apologize to the fans, on behalf of the entire squad."
Adrian also said: "It's time to react, not to talk . Yes, to talk about the pitch. We now have a couple of days to recover from this big setback, but this is the attitude today. It must hurt us all to the core. Not only for having lost a game, which is possible, but for the way we lost.
"The fans must understand that the team is going to give everything, of course. It was a painful night ; a shame for all those who have travelled. We have gone to talk to them to calm things down a bit."
Asked what the fans said to the players at the final whistle, Adrian added: " That the team has thrown its shirt on the ground, that it was a shameful match... We have to accept it, I admit it. From behind, the same thing that they have seen, I have seen it too. It is true that it has been said before, but it is time to learn from this, even if it sounds like a cliché.
"And to move forward, because December is going to be quite intense and we have to be united. Obviously, with maximum self-criticism from the dressing room, from the players and the coaching staff. We are the ones who win or lose. With this way of playing we are not going to get anywhere."