Two in-form play-off contenders meet at the Liberty Stadium but although Swansea edged past Plymouth in midweek, boss Sousa branded the display one of their worst so far this season.
Quoted in the Western Mail, Sousa said: "It’s very important that we are at our best against Forest.
“They are doing very well and we know we have to be on top of our game to beat them.
"But that is what I expect for Saturday’s game, to be at our best again.”
Last season's corresponding fixture ended in a comfortable win for the home side but Forest of course are a much-improved outfit from that which took the field in Wales in August 2008.