Derby lost 1-0 to their local rivals on Friday evening, and their performance was one which fell short of their recent standards.
The Rams failed to reach the top of their game, and ultimately could not break down Forest's well organised defence.
And Clement said: “Clearly we’ve come to a big game as it is our local rivals and we want to do better.
“There wasn’t a lack of effort but it was just the choices that were being made, particularly offensively, that let us down."
Derby had been in brilliant form prior to their match against Forest, going unbeaten in 10 matches, and climbing the table at a rapid rate.
However, Nelson Oliveira struck early in the tie, and Derby failed to make their way back into the match.
The Rams had plenty of possession, but their creative players did not reach the top of their games, and the night ended in disappointment.
The defeat leaves Derby in fifth position in the Championship table, while Forest have moved up to 18th place.