Sir Alex Ferguson's side opened up a seven-point gap over rivals and defending champions Manchester City on Boxing Day after they beat Newcastle 4-3 at Old Trafford.
United have now conceded 28 goals this season, only five fewer than bottom club QPR and more than they had let in by the halfway stage of their title-winning campaigns of 2007, 2008 and 2009.
Ferguson's charges have conceded 40 goals in all competitions and kept just four clean sheets but have managed to secure victories on 11 occasions, despite falling behind in 16 matches.
But Ferdinand is convinced they must tighten up in defence and not always rely on their strikers to bail them out.
"We are concerned. When you are conceding goals at any level you want to put it to a stop," he said.
"This season we have let in far too many goals and we need to change that. We need to make a big effort now to push on.
"We are in a good position but if we are to maintain where we are, we need to sort ourselves out."
Ferdinand's fellow centre-back Jonny Evans echoed those sentiments but he remains confident they will improve in time.
"We know what is going on. Defending is a mindset," said Evans, who scored at both ends of the pitch in their high-scoring win over Newcastle.
"You have to be mentally prepared to defend and want to defend.
"We have been concentrating too much on scoring goals. Instead of getting off to good starts we have killed ourselves a little bit by conceding sloppy goals.
"The good thing is we are scoring, which is the hardest part of football. We have been doing that freely, so I am sure the more simple part of keeping clean sheets will come naturally to us."