United - usually so tight at the back - have conceded a series of sloppy goals in the Barclays Premier League this season.
The latest defensive clanger came against Bolton on Sunday when Zat Knight's effort crept in as Patrice Evra left his position at the far post.
Up the battle: Vidic has bemoaned United's leaky defence
United have not won away in the league this season and defensive hiccups also cost them victory at Everton and Fulham.
Now United skipper Vidic has warned his team-mates to wipe out theerrors as they attempt to keep pace with rivals Chelsea at the top ofthe table.
Victory at the Reebok would have been a huge boost after Chelsea were beaten by Manchester City at Eastlands 24 hours earlier.
Vidic said: 'Yes, we're concerned. Over the last few years we haven't conceded many goals.
'We always looked strong and we didn't give teams many chances. But inthe last few away games we haven't kept clean sheets, which is very disappointing.
Sloppy: Jonny Evans allows Zat Knight to steal in front of him and score Bolton's opening goal
'The results on Saturday were good for us but we didn't win today andnow we don't have the same advantage we had this morning, beforekick-off.
'This was a game we wanted to win and before the game we'd have said a draw would be two points dropped.'
And team-mate Nani has bemoaned United's failure to seize on the opportunity to close the gap with Chelsea to just one point at the top of the league.
The league leaders lost at Manchester City on Saturday while rivalsArsenal also suffered defeat losing 3-2 at home to West Bromwich Albion.
Deflection: Martin Petrov fires Bolton in front - via Darren Fletcher's leg
It meant a win at the Reebok Stadium would have taken the Reds to within a point of Carlo Ancelotti's side.
Nani said: 'We're disappointed because we wanted to win this game, especially because Chelsea and Arsenal dropped points,' Nani told MUTV. 'It was a great opportunity for us, but we drew. We want to fight for that top spot.
'Our rivals lost and this was a good chance to get closer to Chelsea but we still have a chance to get to the top of the league. We now have to look forward to the next game.
'It's always difficult to play at Bolton because they are very physical and strong and play difficult football - they play in the air for their strikers to head the ball. It's very hard but we did well.'
Scant consolation: Nani's super goal failed to lift the spirits after draw
Nani's outstanding solo effort brought the two teams level but even ghis wonder strike failed to bring a smile to the Portuguese.
He said: 'It was a great goal and I'm in good form at the moment but we should have won. That's the point.'
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