Shackleton has struggled for gametime under Jesse Marsch since the American's arrival in February of this year and despite versatility in midfield and at full-back, does not appear to be in the coach's plans this season.
It is hoped Shackleton will feature regularly in south London, as the Leeds academy graduate is at a stage of his career in which sporadic Premier League starts and cameo appearances off the substitutes' bench are insufficient.
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Shackleton made 19 appearances for the Whites last season, but just nine starts and 22 minutes under the new head coach.
His time at Elland Road has been punctuated with minor injuries sustained at inopportune moments therefore he has been unable to nail down a regular starting place.
Shackleton joins Gary Rowett's side who were an outside bet for the Championship play-offs last season.
Leeds United said in a statement: “We wish Jamie the best of luck during his time away from the club.”