McAllister, 24 has become somewhat of a squad player, having been kept out by duo Michael Doyle and Kevin McDonald and due to the recent signings of Danny Higginbotham and Jamie Murphy the Blades need to off-load to satisfy the Financial Fair Play rule embarked on Leagues One and Two clubs.
Blades boss Danny Wilson said: “David needs to play first-team football at this stage of his career. In fact he deserves to play regularly because he’s got a great attitude and is a smashing lad. Unfortunately, though, that’s not something we can guarantee him at the moment and I’ve been honest with the lad and let him know that.”
He made his debut in a 3-1 FA Cup defeat against Aston Villa shortly after signing from Irish side St. Patrick's Athletic and to date has made 18 (+12) appearances and scored four goals for United.