Manchester United manager Sir Alex Ferguson says his side put in their worst defensive display of the season during Saturday's 4-3 win at Reading.
United were particularly fragile at set-pieces and Ferguson says they must improve ahead of next weekend's game with title rivals Manchester City.
"It was the worst defending of this season," said Ferguson. "We need to do something about it.
"Reading's delivery was great but we weren't even competing against it."
United twice fell behind - the first of these representing the 14th time they have conceded the opening goal of a game this season - as all seven goals were scored in the opening 34 minutes at the Madejski Stadium.
Fortunately for the Red Devils they were able to respond twice at the other end of the pitch to secure a win that leaves them three points clear of Manchester City - their opponents at Etihad Stadium next Sunday - at the top of the Premier League table.
An Anderson goal and a Wayne Rooney penalty overturned Hal Robson-Kanu's opener before Rooney's second and a Robin van Persie finish swung the game decisively in their favour following headed goals from corners from Royals pair Adam Le Fondre and Sean Morrison.
There could have been even more goals in the first half had the officials not failed to spot a Van Persie shot that crossed the line before being cleared by Shaun Cummings.
"We deserved to get battered today," said Ferguson. "Nobody competed for the crosses. In fairness Reading have a great delivery of the ball - the boy [Nicky] Shorey whips them in, fantastic crosses but we should be doing better than that. It was terrible.
"If you make mistakes like that defending then you are going to have to do rescue jobs every week. Today was another rescue job.
"It was a miracle that we won the way we were defending. I'm just glad we did win it.
"We have the players that can rescue us and today again Waz [Wayne Rooney] in the first half was fantastic. He and Robin [van Persie] and Ashley Young were a real threat to them, they couldn't control them.
"They were terrific in the first half. Ashley was right back to form and gave them a real hard time of it.
"There are a lot of plus points in the sense that they never gave in and kept going and in the second half showed a great determination to get over the line. That is what it was about today - getting over the line.
"I think the important thing for us is to take lessons from the mistakes we are making and find a solution, because we are going to need it."
Such were United's defensive problems that full-back Rafael was substituted before half-time and replaced by Chris Smalling.
"Rafael had been booked - I don't think there was any danger in him being sent off because it was an innocuous challenge but we really needed to get height into the team," said Ferguson.
"The boy [Rafael] was disappointed coming off. He has been one of our best players this season."