Arsenal manager Arsene Wenger labelled his side "naive" after they lost 1-0 to Ipswich Town in the first leg of their Carling Cup semi-final at Portman Road.
Tamas Priskin's solitary strike ensured the Championship side will lead going into the return leg on 25 January.
"We were too naive. I said to them if you can't win the game at least don't lose it," said Wenger.
"I was very disappointed. We had no spark, no creativity. But I'm confident we will turn it around at home."
Wenger is short of options in the heart of his defence with Thomas Vermaelen and Sebastien Squillaci absent with Achilles tendon and hamstring injuries respectively.
But, despite centre-backs Laurent Koscielny and Johan Djourou's failure to to cut out Colin Healy's ball over the top for Priskin's winner, the Frenchman insisted that the result would not prompt him to buy another defender in the transfer window.
"It would be an easy excuse, we didn't lose tonight because we need a centre-back, we lost it because we didn't produce the performance we wanted," he added.
"We were below our usual level in every department and it would be unfair to put the blame in the defence.
"We have only two central defenders and we are short but I do not want to speak about any particular name."
West Ham United's Matthew Upson, who began his career with the Gunners, has been linked with a return to the club.
Wenger believes that his side's hectic fixture schedule was a major factor in their defeat with Ipswich growing stronger through the match.
"We have nine games in January and it happens sometimes that you don't always play well in every game," he reflected.
"We looked in control in the first half but looked much more vulnerable after the break. I put that down to fatigue."
McParland knew Arsenal would not score
Ipswich caretaker boss Ian McParland admitted that with new manager Paul Jewell in the stands and set to take up the reins for Saturday's trip to Millwall, his own time at the club was at an end.
"I'm leaving but I'll dust myself down and get on with it," he said. "Paul Jewell is an honest lad, I've known him a long time and he will do well here now."
McParland saw his side thrashed 7-0 in the FA Cup third round by Chelsea in the first game of his short stint in charge.
The 49-year-old paid tribute to the way Ipswich responded.
"They sweated blood. They were fantastic and it showed a lot of character to bounce back from Sunday's game. I knew that they were up for it," he concluded.
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