With the top eight players in the world handed a place in the tournament at London's O2 Arena, Isner, who is currently ranked 13th, has significant ground to make up.
However, with two ATP World Tour Masters 1000 tournaments still to play, the 28-year-old has refused to throw in the towel.
"I certainly believe in myself and it would be an unbelievable experience to make that tournament," he told the ATP's official website. "I'm aware of the situation a little bit. The guys that are just ahead of me are actually quite a bit ahead of me as far as points go.
"I do have tournaments and time to try to make that up. I would absolutely love to go there. I've never been there before. So, for me, I've just got to focus and control what I can control. It's a cliche, but take it each match at a time and see if I can put together some good results like I did this summer."
Isner suffered from a number of injuries during the first half of the year, but he has since recovered to string together a handful of positive results on the hard courts.