The midfielder sees his current deal expire on January 8 but manager Micky Adams has decided not to table fresh terms, leaving McAllister free to find another club.
"It's unfortunate that we weren't able to offer Sean more first-team opportunities but that underlines the competition for places we have among the squad," Adams told Vale's official website.
"He's a great professional and we wish him the very best of luck for the future."
McAllister joined Vale on a short-term contract at the start of November but has made just three appearances, two of those coming off the bench.
