The Spireites know they will finish in the top seven if they avoid defeat on Sunday.
But they could still make the play-offs even with a defeat if Dagenham and Redbridge do not beat title challengers Wrexham.
Town go into the game on the back of three successive losses.
“If you watch us at the minute we don’t look like a team that deserves to be in the play-offs,” Cook said.
“The worst scenario, for me, would be to get beat on Sunday and getting in the play-offs. I could not think of anything worse. It would probably make me physically sick to be honest with you."
Cook said he will not be monitoring events at Dagenham and has ‘no interest whatsoever’ in what happens in east London.
“We have got a job to do ourselves, we will get on with it,” he added.
“We need to see a strong performance and a good win, then we can feel like we have earned the right (to be in the play-offs).
“The reality is we have been very, very poor over the last few weeks.
“What you have got to believe is that on Sunday we are going to turn a page.
“We need to put in a performance that makes our supporters proud.
"We go into this game on Sunday with a chance to be in the play-offs. We can then go into a knock-out sequence of events which can see you promoted. So at the minute nobody knows how this story and this book ends. At the minute the story is not going very well for us at all but it can change a lot by Sunday and going into next week.”