The 24-year-old is still to convince United manager David Moyes that he is worthy of a regular starting berth, although he impressed in last weekend’s 2-0 defeat of Swansea City.
Kagawa will face renewed competition for his preferred central playmaking role when Wayne Rooney returns to fitness, but he says he has identified the areas of his game where improvements are needed.
“I think I can still improve my strength,” he told the United website.
“I’m not the tallest or biggest player, so I have to move my body more. Smaller players in the Premier League are very good at using their bodies and that’s what I will continue to do.
“I realise the Premier League is a very tough league and I know I have to be stronger.”
Kagawa joined United from Borussia Dortmund in 2012 and won the Premier League title in his debut season at Old Trafford.
“He’s such an intelligent and creative player that he makes everybody around him play well,” said United assistant manager Steve Round.
“You can always find him, he always retains the ball, can turn and go forward, is intelligent, and his creativity is terrific.
“He’s a really good kid as well. He has a great sense of humour and a tremendous work ethic. There’s never a moment’s problem with him because he’s such a terrific professional.”