Hackett, 65, will spend his last six months in the role handing over the reins to Riley, who has ended a 20-year career as a referee.
In his final season, the Football Association was forced to defend Riley after Everton manager David Moyes questioned his appointment as the replacement referee for his side's FA Cup semi-final against Manchester United.
Moyes called for an FA investigation into whether the official had any allegiance towards United.
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