The Reds have won just two of their last 20 matches, but McClaren knows all about the threat they can pose because of the sides' last meeting.
He feels that Derby's toughest test of the season came at the City Ground, where the two sides battled out a 1-1 draw, and he is predicting a similarly tough examination of his squad's qualities tomorrow.
"The last memory of the fixture I have got is from the City Ground back in September and that was our toughest game of the season," he said. "It was a real battle and it was a great atmosphere.
“Every game I sit here and say that it is tough opponent. Forest are exactly the same. It’s a local derby, it’s a big game for the supporters and we have just got to treat it as normal."
Since the two sides met back in September, their seasons have gone in different directions and anything other than a Derby win tomorrow would be an upset.
Stuart Pearce's side are 10 points outside the play-off places and defeat to Derby could cost their manager his job, according to the Daily Mirror.