Manager Mixu Paatelainen thought Dundee United were "absolutely rubbish" in their 5-0 loss to Celtic.
The heavy defeat in Glasgow leaves the Tannadice club five points adrift at the bottom of the Premiership.
"Everybody in that dressing room must look in the mirror," Paatelainen told BBC Scotland after his second match in charge.
"It doesn't matter about tactics or shape, if you don't get the basic fundamentals right."
United fell behind to a Leigh Griffiths strike after 15 minutes, with Dedryk Boyata adding a header before a Kris Commons brace and Scott Brown's late strike.
The visitors were repeatedly torn apart by the league leaders and posed little threat in attack.
"It doesn't matter what you do on the training ground, if it doesn't happen out there on the pitch," added Paatelainen, who was brought in to replace Jackie McNamara.
"All that goes in the bin!
"No wonder we are where we are. It was so disappointing."
United have lost four games on the trot and must now pick themselves up for next weekend's home meeting with Ross County.
"It's difficult to say if it's a confidence issue," added the exasperated former Finland boss. "I think we just don't realise what we must do.
"We pinpoint the dangers that Celtic will throw at us, we want to make sure that doesn't happen, that we eliminate them.
"But if you are not switched on in certain situations, you are letting good players like Celtic have do what they do best."
Paatelainen is adamant that he can turn the struggling club round but is warning that it won't happen overnight.
"I always knew it was a big job because the team is not playing well," he explained.
"There is plenty to improve on. An unbelievable amount - from defending to attacking.
"We can't tolerate these kind of standards.
"What we can do now is make sure that we every day we do our best. It won't happen in a flash. It will take time because we are low."