Derby first-team coach Liam Rosenior admitted everyone had to "look in the mirror" after a 2-0 home defeat to Barnsley left them bottom of the Championship.
It was Derby's fifth home defeat of the season and increases the pressure on manager Phillip Cocu who was not at the game because he was self-isolating after the club's chief executive tested positive for Covid-19.
Derby have now gone nine home games without a win in the Championship and Rosenior, who was in constant contact with Cocu throughout the game, said: "I think the performance summed up the start of our season.
"The manager is a big man and will take responsibility but we all need to take responsibility too and I include the players in that – we need to look at ourselves in the mirror.
"Trust me, I go home tonight and I'm not sleeping because it hurts."
Derby desperately needed a result but a mistake by David Marshall in the 30th minute left them chasing the game when his clearance went straight to Conor Chaplin, who scored with a low drive.
Jason Knight saw an effort cleared off the line and Martyn Waghorn curled a free-kick just over but Derby could not build any sustained pressure and Barnsley were always dangerous on the counter.
Callum Styles fired wide in the 67th minute and Chaplin wasted another great opening after Derby's defence was cut open again.
But any chance the home side had of making them pay vanished in the 83rd minute when Barnsley broke quickly and Victor Adeboyejo advanced to the edge of the box before curling a low shot past Marshall.
Rosenior added: "I think we were over-anxious maybe to win the battle, we've got good players and when you are low on confidence, you need to remember that you are a good player.
"I can't afford as a coach to make excuses about mistakes because this is 11 games now so I have to look at myself, everyone at the club needs to look at themselves, this is a huge football club and we are not doing it justice.
"There's no way this club should be in the position it's in and I have to hold my hands up to that as well."
Barnsley have won three of their last four league games to sit 16th in the table and head coach Valerien Ismael hailed a "perfect afternoon".
He said: "It was a big win for us, first of all for the attitude, the performance from the team. We wanted to be aggressive and have high intensity in the game.
"I told the guys before the game, 'force mistakes, punish mistakes', and it was a perfect game plan for us that's why I'm very happy about the result, the performance and I'm told the first win since 2009 against Derby – that's why it was the perfect afternoon.
"We knew Derby with their confidence was very, very down and in such a situation you have to be ready to force the mistake.
"There is a long way to go, we have to work hard, we don't have the big roster like Derby or Cardiff, we know what we have to do to get the points all the time.
"We work hard together and now this gives us confidence and more belief in our principle to transfer to the team and the team transfers this on the pitch."
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