Nottingham Forest signed Simon Cox and Billy Sharp during the summer and Clough has acknowledged that they will be much better opposition than the side Derby beat 2-1 last season.
Clough told the Nottingham Post: "Forest are a much-changed and better side than 12 months ago. They have brought players in and spent a few quid.
"We are happy with our front players, but in Cox and Sharp, as well as Blackstock, they have as a good as strikeforce as any in this league and possibly in the bottom half of the Premier League."
Derby currently sit 17th in the Championship table.