On Sunday, he is expected to make his full Premier League debut for Newcastle against Chelsea.
"I was 22 when I got the offer," Muto told the Daily Mail.
"At the time I didn't feel the manager of the club really wanted or needed me. They wanted to get young players with potential and then loan them out.
"Instead of doing that, I wanted to stay at my club to help me progress. I wanted to feel like I could make my own progress step by step, so I didn't take that opportunity.
"You don't get confidence quickly, it only comes through doing things little by little."