Kagawa only made 14 starts in the Premier League last term in what was a miserable campaign for the Red Devils.
He said: "When I look back, last season was tough.
"I will use that frustration as a trigger to express myself this season, challenging myself to do new things.
"I'll work hard to achieve goals and results. I'm really enjoying myself, it's my third year with United and I know my team-mates very well.
"We've learned a lesson from last season. It is important for us to stick together and work towards the same goal.
"We can do much better if we can bring out the best of ourselves. We want to keep succeeding in the manager's new system, and we want to win trophies. That's what the fans expect."
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