The 23-year-old ended a five-year spell at Craven Cottage in August when he embarked on a new career at the Madejski.
He said: "I would have loved to have played for Fulham for longer and pushed on and played for England, which was the plan.
"My game as a full-back is about getting forward but the way Lawrie wants his team to play, I don't think Fulham would have got the best out of me.
"I'm an ambitious lad. I want to be playing for England and I want to be playing in the Champions League when I'm 25 or 26.
"I've made no secret of that and I don't think that would happen if I had stayed at Fulham under Lawrie."