Jay Bothroyd has returned to parent club QPR following the expiry of his loan spell at Sheffield Wednesday.
The 30-year-old teamed back up with Owls boss Dave Jones when he joined Wednesday in August and made 14 appearances for the Owls, scoring one goal.
Jones confirmed earlier this week that he would not be looking to extend Bothroyd's stay at Hillsborough, while QPR manager Harry Redknapp is keen to boost his firepower as he looks to mastermind the London club's Barclays Premier League survival.
Bothroyd, who spent over two years at Cardiff from 2008 while Jones was in charge of the club, has not featured for the Owls in their last seven matches and scored his solitary goal for them in the 1-1 home draw with Leeds in mid-October.
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.
