Harrison has won a first call-up to the England U21 squad this week.
He said: “I was 13 when my mum came up with the idea of me going to boarding school in America to improve my education while I played football. It was just a backup plan, if anything went wrong in football.
“I got a scholarship at the Berkshire School in Sheffield, Massachusetts. I then went to Wake Forest University but was only there six months before I got drafted by Chicago. New York then traded up to get me, and this is my second season playing professionally for them.
“I was really apprehensive and didn't want to leave United. Everyone in that system is just tunnel-visioned and just thinking about making it to the first team but a lot of players don't.
“Man U were disappointed. They didn't want me to leave. They didn't think I would ever go to America to play football."