A group of Manchester United fans unhappy with the club's involvement in the abandoned Super League plan gained access to their training ground on Thursday and spoke to manager Ole Gunnar Solskjaer and some members of staff.
The protesters carried banners with messages including "Glazers out," in reference to the Glazer family who own United, and "We decide when you play."
The protest, reportedly involving around 20 people, was held at United's Carrington training complex.
British broadcaster Sky Sports reported Solskjaer's assistants, Michael Carrick and Darren Fletcher, and midfielder Nemanja Matic were among those who also spoke to the group.
"Buildings were secure and the group has now left the site," United said in a statement.
United were one of six English teams who signed up to join a breakaway Super League also involving three clubs from Spain and another three from Italy.
The English teams all withdrew on Tuesday under pressure from the British government and supporters.
Earlier, Manchester United co-chairman Joel Glazer apologised to supporters for the club's involvement in the hapless breakaway project, saying the hierarchy failed to show respect to the "deep-rooted traditions" of the English game.
"Although the wounds are raw and I understand that it will take time for the scars to heal, I am personally committed to rebuilding trust with our fans and learning from the message you delivered with such conviction," Glazer said in an open letter to supporters on Wednesday.
"We continue to believe that European football needs to become more sustainable throughout the pyramid for the long-term. However, we fully accept that the Super League was not the right way to go about it."
Australian Associated Press