The 24-year-old moved to Old Trafford from Bundesliga giants Borussia Dortmund last summer but suffered a major knee injury early in the season.
However, he showed glimpses of his talent, netting an impressive hat-trick in a comfortable win over Norwich, and he is keen to re-find the form that saw United part with €20 million to sign him.
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"You have to believe in yourself. If you don't, things can go wrong both on and off the pitch. Being positive and believing in yourself is important, not only in football but also in improving as a person."
New Manchester United boss David Moyes has a host of attacking options at his disposal including Robin van Persie and Wayne Rooney and Kagawa says he relishes playing alongside such quality players.
"It is inspiring and exciting to play alongside such world class players," Kagawa continued.
"Wayne can do everything to the highest standard. He has everything a football player would need: team spirit, hard work, switching between attack and defence.
"You don't see such players very often. He plays for the team, plus he can score and assist. There is so much I can learn from him and I enjoy playing with him. Robin, of course, made the difference with his goals. He's wonderful."