The Scotland under-21 international has been with the club since August 2007, after joining from Motherwell, didn't make a senior appearance.
Alan has had loan spells with Barrow and Accrington Stanley.
The 22-year-old's contract was due to expire at the end of the current season, but he is now free to join another club and pursue his career elsewhere.
Leeds United have cancelled the contract of striker Tom Elliott.
The 21-year-old spent the first part of the season on loan at Rotherham and has been training in Scotland over the past week. He is now free to pursue a career elsewhere.
Leeds-born Tom made history in February 2007 when he became the first recorded to schoolboy to play in the first team after Dennis Wise handed him his debut as a substitute at Norwich during our Championship relegation season.
Since then, Tom has started just one game for the club and made two further sub appearances.
The majority of his experience has come while on loan, and he has had spells with Macclesfield, Bury, and Rotherham.