Summer recruit Paul arrived at the club from Leeds United and has impressed since returning to training from being England's number two at the European Championships.
However Kasey, on international duty for USA during the summer, has incredibly played almost 100 successive first team matches - an ever-present record stretching back to the end of the 2001-02 season.
Both keepers have been in fine fettle during a long per-season campaign and now there are just two matches left for Jacques Santini to make his mind up.
"There is a serious battle going on," said coach Hans. "Kasey has played for the last two seasons non-stop in the first team, Paul has to prove himself but Kasey also has to prove himself all over again.
"It is a new management, completely new staff so the goalkeepers start from scratch.
"So far, almost four weeks into the season, both are in great form, both are great trainers and the battle is on.
"It will be an interesting decision the gaffer has to make when we play Liverpool. One thing I know for sure, one goalkeeper is going to be very disappointed."
Hans insisted that despite the intensity between the two to line-up against Liverpool next weekend, the pair have developed a typically 'goalkeepers' union' friendship.
"Every Premier League club has two quality goalkeepers and they have to fight it out for the number one spot," added Hans.
"We always say in the goalkeepers' union that we are the best of friends but the greatest of rivals. I see that on the training ground. They are working great together but both want to be first choice for Liverpool."
Hans Segers says there is a 'battle royal' developing for the goalkeeper's jersey between Paul Robinson and Kasey Keller.