Sir Alex Ferguson has warned Manchester United that they need to improve their defending or risk disaster against Manchester City on Sunday.
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Ferguson, 70, said he is struggling to remember when United conceded more goals at this stage of a season. United conceded three goals at Reading on Saturday, have let in 21 in the Premier League and 32 in all competitions and Ferguson has been critical of his team for both the total and the manner of the goals conceded.
Reading struck twice from corners in United's 4-3 victory at the Madejski Stadium and the United manager believes his side are struggling against aerial balls.
Ferguson said: "I think we are getting punished when the ball gets in our box at the moment but we should still be defending far better. Reading did produce some fantastic balls into the box but we should be expecting better. It's a worry, it's a concern. If we perform like that on Sunday then God knows what is going to happen to us.
"You see the goals against. We have lost 32 goals this season and I can't ever remember us losing so many goals before Christmas. So it is a concern: no question about that."
City beat United 6-1 at Old Trafford last season and Ferguson admitted he is worried about taking on such a sizeable side when his own team have set-piece frailties.
"They can play with Balotelli and Dzeko, all really tall players, so it is going to be a big challenge for us on Sunday," he said.
Former United captain Gary Neville had said a problem is the reluctance of goalkeepers David de Gea and Anders Lindegaard to come out and command their six-yard box, but Ferguson insisted this was not the case, instead pointing to the marking of his defenders.
"[The opposition] are still getting free headers," he said. "That's the issue and we have to arrest that."