They had banners saying ‘Glazers Out’ and ‘51% MUFC’.

Co-chairman Joel Glazer would have been a vice-chairman of the European Super League beforeUnited withdrew on Tuesday after a furious backlash.

On Wednesday, he issued a letter of apology admitting the club made a mistake joining the proposed breakaway competition.

“At approximately 9am this morning a group gained access to the club training ground,” said United in a statement.

“The manager and others spoke to them. Buildings were secure and the group has now left the site.”

Solskjaer was joined by coach Michael Carrick, technical director Darren Fletcher and midfielder Nemanja Matic in speaking to the fans, who were pictured at the security entrance, outside the main entrance and on a training pitch.

United were one of six Premier League clubs to sign up to the European Super League, before they all withdrew within 48 hours of the competition being announced.

“We failed to show enough respect for its deep-rooted traditions,” Glazer said in an open letter to fans.

There has been a long-standing campaign against the Glazer family since the Americans’ controversial leveraged takeover of the club in 2005.