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29th August 2016
11:38am BST
McKenna issues instructions to his youth players[/caption]
McKenna, 30, started his career as a midfield player for Enniskillen Town in Northern Ireland.
He joined Tottenham as a player but a hip injury brought an end to his playing career and he switched to coaching.
He has been managing Spurs' Under-18s side, which reached the semi-final of the FA Youth Cup in 2015, before losing to Chelsea.
His brief at United will be to help restore the club's academy to a regular source of players for the first team.
The most famous cohort is the so called Class of 92 which saw players including David Beckham, Ryan Giggs, Paul Scholes, Nicky Butt and the Neville brothers graduate to the first team and become the backbone of the squad for well over a decade.
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