Carlo Ancelotti was left "disappointed and angry" after watching his side concede a late equaliser against Everton and miss the chance to end their recent slump.
The Blues have now won just once in their last six league games but appeared on course to go back to the top of the Barclays Premier League thanks to Didier Drogba's 42nd-minute penalty.
But Everton substitute Jermaine Beckford headed home four minutes from time to hand David Moyes' men a point.
"I am disappointed and angry," said Ancelotti. "Not just because of the result.
"We played good football in the first half and the second half was totally different. We played the long ball. We were a little bit scared. I didn't like this.
"We are working to play a particular kind of football and I don't understand why we have changed it. We have to look at it and I have to understand and change it."
Ancelotti believes that with hard work, however, Chelsea can regain their all-conquering form.
He added: "We have to do better day-by-day on the training ground, in the training sessions. We have to work harder than we are doing. This is the way I know to move on in a difficult moment.
"I am worried yes, because we haven't won a lot of games. The second half was totally wrong. We have to do better."
