Manchester United manager Sir Alex Ferguson was left "flabbergasted" by his young side's performance after their Carling Cup exit to Coventry.
The Sky Blues won through 2-0 and Ferguson said: "I did not expect that at all. I am not interested in giving reasons or mitigating circumstances.
"We have trumpeted these young lads a lot, so what has happened tonight was a big shock for us all.
"We didn't cope with the battle at all - it was just a very bad performance."
The Scot made 11 changes to the side that beat Chelsea at the weekend, with the likes of Jonny Evans and Danny Simpson handed their senior debuts.
But the reshuffle backfired as the hosts' lacklustre display was punished by a fired-up Coventry side.
Ferguson added: "You want to give these boys a chance and we have not had the opportunity to do that until tonight.
"Some of those players have got good ability but that was very disappointing, believe me. All we can ask now is that they learn from this very quickly."
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And he refused to talk up the benefits of a reduced workload on his squad in what could be a long hard season.
"I'm never happy to lose, nor to go out of a cup," he said. "That is absolutely not an issue at all."
Coventry manager Iain Dowie, meanwhile, was understandably delighted, insisting his side's win was anything but a "smash and grab" effort.
"Our display was full of heart and desire, but we didn't come to shut up shop - we passed well, created chances and put pressure on United," he said.
"They may have made changes but in Anderson, Nani, Michael Carrick, John O'Shea, Wes Brown and the rest they had tremendous players who cause you 100 problems in 100 different ways.
"But we kept our shape well, our ball retention was good, and we refused to show too much respect."
And he urged his side to take their performance into Saturday's league tie against Charlton.
"I knew I would get a response after Saturday's 4-1 defeat to Ipswich, and the team deserve to be applauded. Now we want to take this into the league, starting with Saturday's tie against Charlton, because that's what our bread and butter is."
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