Chelsea's recent form has looked "kind of horrible" due to the high standards expected at Stamford Bridge, says manager Thomas Tuchel.
The Blues have won once in their last four matches in all competitions and conceded three goals in both their previous two fixtures.
Prior to their defeat at West Ham and draw at Zenit St Petersburg, Chelsea had conceded just 10 goals this term.
"This is very unusual for us and this should not become common," Tuchel said.
He added: "The performances are not horrible or bad. They are in some moments average, and average looks kind of horrible when you play and work for Chelsea.