Manchester United signed Spector from Chicago Fire in 2003, and the teenager went on to make his first-team debut the following year.
The ex-United States international only made eight appearances under Ferguson before joining West Ham permanently in 2006.
The 33-year-old has just joined Scottish outfit Hibernian, and has revealed a meeting with the famous manager that took place after his first match in a United shirt.
“I was incredibly fortunate to learn from arguably the best manager in the world – in any sport,” Spector told the Daily Record.
“Sir Alex Ferguson and Roy Keane were blunt, they were honest and those were things I respected.
“I played in a reserve game at Middlesbrough, and it’s fair to say I had a poor game.
“I was back in with the first team that weekend but I didn’t even make the bench and the manager pulled me aside after his team-talk.
“He said ‘Spector — you were absolutely useless the other night’.
“That was it. There was no hairdryer. I was like, ‘Yeah, I know. It won’t happen again boss’.
“He knew how to get the best out of each individual.
“He didn’t treat everyone exactly the same. Even at his age, he was able to relate to me and understand me as a person.”
“I’ve never played for anyone that has understood that or enacted that better than Sir Alex Ferguson.”
Spector had long spells with both the Hammers and Birmingham before returning to the US with Orlando City prior to joining Hibs.
The 33-year-old was also asked who his best team-mate was at Old Trafford, and he chose to name a fellow midfielder.
“I have also been incredibly fortunate to play with some of the best players who have ever played the game — and to learn from them,” Spector added.
“It would be easy to say the best was Cristiano Ronaldo but, to be honest, I’d have to say Paul Scholes.”