Sir Alex Ferguson described Manchester United's 3-2 home defeat by bottom club Blackburn as "a disaster".
After battling back from 2-0 down, United were dealt the final blow 10 minutes from time courtesy of a goal from Grant Hanley.
"It is a disaster," said the United manager, whose side failed to replace Manchester City at the top of the Premier League on his 70th birthday.
"I never expected it. We lost two terrible goals and you can't do that."
United fell behind to two strikes from Yakubu, either side of the break, before Dimitar Berbatov hauled his side back level with two of his own in quick succession.
However, Blackburn stunned United late on, when 20-year-old Hanley beat keeper David de Gea to Morten Gamst Pedersen's corner, and again rose highest to head in the follow-up.
"We all could have done better," he said, when asked about De Gea. "It was a bad goal to lose.
"At 2-2, I thought we were going to win it. It looked like the momentum was with us, but that third goal was a killer."
Ferguson pointed to the injuries in defence that forced him to field senior players out of their usual positions.
"We've had problems with four central defenders out," added the Scot. "We missed Michael Carrick's craft in the middle. We played Park Ji-sung and Rafael in centre midfield, but they aren't centre midfielders.
Phil Jones, who moved back into central defence from midfield as a result of injuries, was more critical of the defeat by his former club.
"I am gutted," he said. "[And it was on] the manager's birthday as well. We weren't at the races. Too slow, too laboured. Not quick enough.
"The injuries don't help. But they are no excuse. We were nowhere near good enough.
"They punished us and they thoroughly deserved their win. It will be a bad New Year's Eve.
"I feel worse today than when we got smashed 7-1 last season playing for Blackburn. That puts into perspective how disappointed I am."
Rovers boss Steve Kean was delighted with the victory which follows the draw at Liverpool last week.
"To come to a place like this and get a result is up there with our best," he said, with his club going into 2012 off the bottom of the table.
"As soon as it went to 2-1, we were thinking it was going to be tough. And at 2-2, it would have been a good point."
Kean, who some fans of the club want to see leave, paid particular praise to the young players, such as scorer Hanley, Adam Henley and Josh Morris.
"We built on what we did at Anfield [1-1 draw against Liverpool], although maybe the side was a little bit younger today," he continued.
"The lads that came through the academy, along with the senior guys, can all take credit.
"We're going through a transition period. We have new owners and although I'm not new to the club, I'm new to the position.
"We're trying to integrate the young players and develop the backbone of the club."
Hanley, scorer of the winner, said the young Rovers team have had to "grow up quickly".
"It was a great result today," he commented. "We got the organisation and shape right.
"Playing in games like this is good for the young boys. It puts them under pressure early and forces them to grow up quickly."