The 22-year-old made just one first-team appearance for the Red Devils which came in the Europa League in 2019.
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Galbraith previously spent the 2021-22 season on loan at Doncaster, featuring 36 times for the League One outfit.
This campaign has seen him turn out for Salford City, who are owned by owned by Man United legends Gary Neville, Nicky Butt, Phil Neville, Paul Scholes, David Beckham and Ryan Giggs.
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The midfielder, who was once dubbed 'little Iniesta', has become a forgotten man at Old Trafford.
Northern Ireland international Galbraith joined the Red Devils from Limerick six-years ago.
And now he has confirmed his departure, taking to social media to thank the club for the opportunity.
"After 6 years, my time has come to an end with this magnificent club at Manchester United," he said.
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"I want to thank the club, coaching staff and players for helping me become a better player, a better person and for making me feel at home.
"My earliest ambition as a boy was to become a professional footballer and I'm forever grateful to the club for giving me the opportunity and support to fulfil that dream.
"It's been a privilege and I feel very fortunate to have been able to represent the club.
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"I step into the next chapter of my career a more mature well rounded person and I'm excited for what's next…"
Northern Ireland manager Ian Baraclough previously described Galbraith as their Iniesta or Xavi.
"Not to put too much pressure on his shoulders, but he's our little Iniesta or Xavi," Baraclough said back in 2020.
"[He's] someone who can get on the ball and manipulate the ball and find positive passes.
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"Over the coming years, he will give us a different flavour to the squad."