Police were called to Manchester United's training ground on Friday after a group of supporters arrived to protest against the club's owners, the Glazer family.
United were forced to lock the front gates at Carrington and divert visitors to a back entrance after a group of around 30 fans carrying "Glazer Out" banners gathered outside the complex at around midday.
It comes a year after protesters succeeded in breaking into Carrington before speaking briefly to former manager Ole Gunnar Solskjaer.
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