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The 19-year-old, who signed a new contract until the summer of 2013, made one start and seven substitute appearances this season.
Dons chief executive Erik Samuelson told the club's official website: "Brendan is a talented player and (manager) Terry Brown had earmarked him as part of his long-term plans.
"That is why we offered him an extended contract in January, which he signed.
"However, Brendan now wishes to leave the club and we have decided not to stand in his way. We are seeking a fee for his transfer."
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