Midfielder Lampard refused to pull his punches in his appraisal of the Blues and admitted they let their standards drop after their historic comeback against Napoli two weeks ago.
That win saw Chelsea set up a clash with Benfica, who they will face tomorrow in the first leg of their last-eight tie.
Since beating Napoli, they have reached the FA Cup semi-finals but have taken just one point from two Barclays Premier League games to slip five points behind fourth-placed Tottenham, who drew 0-0 at Stamford Bridge on Saturday.
Lampard told Chelsea TV: "The fixtures and where we are in the table doesn't lie - we're not as good as we used to be.
"We used to have a fortress here and, for whatever reason, we're just not doing it. It's something we must all put right."