The Scot, who appears regularly on the club's official television channel, also claimed that the news 'caught him by surprise'.
"It really has caught me by surprise. My phone kept ringing all morning and I thought it must be something serious," he told MUTV.
"When the news comes through, it's about the manager... which is serious if you're a Manchester United supporter. Everybody will be a little bit concerned. Can the next guy coming through the door do what Sir Alex has done? That's going to be tough."