In 1980 at 33 years of age, Knox was player-manager at Forfar Athletic when Ferguson asked him to join him at Pittodrie. It didn't take him long to say yes and join the great man before moving with him to Manchester United six years later.
"I was player-manager of Forfar and Alex turned up at Station Park for a reserve League Cup-tie on Tuesday night," Knox, who also managed Dundee and the Scotland U21s amidst his assistant's roles, told SunSport.
"He said 'How do you fancy coming up as my No2?'
"I told him I was up for that and he said 'Right, when can you start?' "I told him I'd start the next day if he wanted me to.
"He said, 'Fine - come up and we'll get everything sorted out in the morning.'
"That was it. I drove up the next morning, signed my contract and watched the game against Twente Enschede that night.
"I think Jim McLean had recommended me because I'd been taking the reserves at United towards the end of my playing days.
"Going to United was the same. I was taking Aberdeen training one afternoon at Deen Park and saw his car reversing up to the park. My mother hadn't been well and my initial thought was that he had bad news.
"But he came over and said, 'Right, we're going to Manchester United'. Then he'd a think about it and said 'Mind you, Dick Donald will offer you the Aberdeen job. What do you fancy doing?' But again, I said I'd come with him."