"We will be very difficult to beat if we can play to that level for the rest of the season," Cox told the Nottingham Post.
"As long as we are hard to beat, we will be okay. And we were more than hard to beat on Tuesday.
"We played some good football and, if we can produce that standard regularly, we will do well. In fact, we played some magnificent football. The lads were superb."
Cox was announced as a Forest player on August 11.