The 21-year-old agreed a one-year extension to his St James' Park deal before securing a season-long switch to link up with former Newcastle winger Stephen Glass at Aberdeen.
Former head coach Steve Bruce described it as a 'great opportunity' for Longstaff, but a January recall is on the cards with the midfielder making just five appearances so far.
Longstaff has been left out of the Dons' last two matchday squads, with Glass recently declaring the club were expecting 'better performances' from their summer signing.
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