The Premier League leaders have fallen behind on 16 occasions in all competitions this season but are seven points clear of Roberto Mancini's side
United currently sit top of the Premier League, but have conceded 28 goals in their opening 19 games and have fallen behind on 16 occasions in all competitions this season.
The Boxing Day 4-3 win over Newcastle was just one of a number of times United have had to rely on their attacking talents to compensate for defence frailties, and Ferguson is concerned over the worrying trend.
“I can’t answer it,” Ferguson told reporters. “I can’t possibly answer it. We’ve analysed it to every possible detail to try to get a constant thread that tells me how to address it.
“It’s either don’t attack at all, which is not going to be Manchester United, or let our supporters live through the agony of 4-3 wins. We’ve not had a 5-4 yet or a 6-5. I think that could be more exciting.
“I said after the Reading game [United won 4-3] that it has to stop and it hasn’t. I say it again, but it won’t stop. This present team, it’s just one of those seasons we just seem to be letting in silly goals.”
“It does matter, of course it matters. If we’re scoring four goals at home there should be one against us or nothing.
“That’s one way to help your goal difference. So that’s always a concern. The concern for me about losing goals is that it’s testing us to the very limit and making us play beyond the energy levels we need to.
“In home games we should be in control. In the Sunderland game we were 3-0 up, we should put the tools away, but they get a goal back. They found the energy when we stopped using ours. That’s the lesson about this Premier League. You can’t do that in this league, it is too competitive.”
Ferguson believes an inconsistent line-up in defence has likely contributed to the club’s weakness at the back, with first-choice centre-back Nemanja Vidic only able to make a return from injury during the past two weeks.
“We’ve not had the same back four in more than two or three games in a row,” he added.
“Chris Smalling played at right-back the other night and played centre-back the previous game.
“Nemanja Vidic played on Saturday, but then Rio Ferdinand played the following game. Phil Jones played on Saturday. The only one to have played consistently is Patrice Evra.
“That has to have something to do with it. What we need to look at now is what is the consistent partnership we want to give us that solidity at the back and to enjoy our game more.”
However, despite the high number of goals conceded in defence, United find themselves seven points clear the season’s mid-way point - a lead which surprises Ferguson.
“It’s such a tight league you never expect that,” he added. “We always say if you can get to new year and be there or thereabouts, you will be in the running.
“If we can maintain the lead we have until the FA Cup game at West Ham, we’ll be delighted.”