Disappointed David Wagner surveyed Huddersfield's Town's 3-1 setback at Preston North End and admitted: "Our fighting attitude and workrate wasn't good enough."
A second successive defeat inflicted by Town old boy Tom Clarke, Alex Baptiste and Paul Gallagher (Nahki Wells replied late on) left Town fourth in the Championship.
And Wagner said a big improvement is needed when Derby County head to the John Smith's Stadium on Saturday.
"We weren't nearly at our normal level, especially in our first line. If you want to be successful against a side like Preston, you have to be aggressive," added the boss.
"At the end, set-pieces decided the game, but credit to Preston, because they delivered them very well and converted them well.
"Paul Gallagher uses set-pieces very well, this is well known, and we were not able to defend them, this was a weakness for us in this game."
"Now I have to find the right solutions for Saturday because we have to come back to what we have done in our previous games."
