United are currently five points behind Chelsea in the Premier League.
Ferguson told the club’s official magazine, Inside United: “This present team doesn’t kill off sides as well as they should.
“At Goodison, we had three or four chances at 3-1 to really put the game out of sight, but we were wasteful and ultimately paid the price.
“We threw away two goals in injury-time. That’s unthinkable.
“That killer instinct just isn’t there at the moment and it’s something we need to develop.
“We haven’t had a problem scoring goals.
“We got three against Liverpool, Everton and West Ham, two away at Fulham, three in the Community Shield; that suggests we don’t have difficulty finding the net.
“What we’re not doing, though, is killing teams off.
“I have no doubt the players have taken these setbacks on board. They suffer just as much – if not more – than the rest of us.
“They’re the ones throwing the points away and they’re the ones who know fine well that they’re good enough to win this league.”
He added: “We’re playing well, and perhaps those four points we have dropped away from home at Fulham and Everton have given off something of a false impression.
“Nevertheless, we didn’t like letting those points slip away and it’s crucial that we don’t make too many more similar mistakes this season.”