The keeper played seven times for United – once in the Premier League, five in the League Cup and once in the Champions League.
Amos told The Sun: “Sir Alex had faith in me and gave me opportunities at 18. I'll be eternally grateful for that.
“He kept a distance from his players. He worked on that fear factor – including with the senior players.
“But, at the same time, he could crack a joke with you.
“Sir Alex kept everyone guessing and you were always on your toes – even if you were a world-elite footballer."