Kagawa joined United from Borussia Dortmund this summer.
He told manutd.com: "I was totally amazed by how many fans came out in South Africa and China, and how loud they were! It made me realise that United supporters are all over the world. It dawned on me how big a club United is and I feel very proud and lucky to be a part of this club.
"I understand what I should be doing in training because most of the football exercises are easy to understand. I know my English is not good yet so I will study hard so that I can communicate with my team-mates directly as soon as possible."