Manchester United boss Ole Gunnar Solskjaer spoke to fans who entered the club's training ground at Carrington on Thursday to protest against the Glazer family's ownership.
They had banners saying 'Glazers Out' and '51% MUFC'.
Co-chairman Joel Glazer would have been a vice-chairman of the European Super League before United 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.