Lopes joined City as a teenager.
He told the Athletic: “When I went there, I saw it as a great opportunity for me and I had my first pre-season with the first team at 16. But I wanted to be a professional playing regular football. I wanted a different challenge and to play every weekend.
“I knew it was difficult in City because they had a lot of money and had big players at the club. I spent three years at City and enjoyed it.
“When I scored that goal against Watford, I was really happy. Everyone was praising me and it was a big moment, one of the best in my career.
“But at the same time, I knew it wouldn't change anything because I knew the players at City at the time, I knew the money involved.
“I knew in my head that to play more, I would have to leave. I could have stayed but it would have been more for the under-21 team than the first team."