The left-back was forced off after 64 minutes at the Walkers Stadium on Friday night following a heavy challenge that also left him with a calf injury.
"It`s disappointing for the lad and the team," City boss Keith Millen told the club`s official website.
"We were hoping it wasn`t too serious but now the scans have revealed a fracture."
McAllister added: "It is one of the most painful injuries I have ever experienced."
Source: PA
Source: PA