Chelsea's England midfielder Frank Lampard has warned his team-mates they cannot afford any more basic defensive errors when they face Manchester United on Sunday.
The Blues' indifferent form in recent weeks has seen them slip three points behind leaders Liverpool at the Barclays Premier League's summit.
Lampard said: "The errors have been very frustrating for everyone involved because we do work on them in training anyway."
He continued: "Sometimes it has been an individual error or a collective one, but it has been very important because we have dominated the last two games and we lost out on a set-piece in the final minute each time.
"We can't afford to let that happen against a team of Manchester United's calibre."
Chelsea have conceded costly goals against Liverpool, Roma, Arsenal, Bordeaux and West Ham during the past three months.
Late goals in their last two games against Fulham and Southend have increased Scolari's concerns.
Scolari has now added England Under-21 defender Michael Mancienne to his squad after a two-month loan spell with Wolves.
But Mancienne has not ruled out a further loan period in the build-up to the Under-21 European Championships this summer.
Mancienne is certain to be part of England's squad for the competition and he said: "I need match fitness coming up to the Championships. But I am now where I wanted to be at 21 - around the Chelsea first team but also playing first-team football as well by going on loan and getting experience."
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