The Japanese international started his United career brightly following his summer transfer from German champions Borussia Dortmund.
However, a knee injury kept him out of action for two months and since his return his performances in the United midfield have been criticised by some quarters.
Ferguson is not concerned though and has instead insisted that the 23-year-old will come good once he has adapted to the Premier League.
"He's come from an environment that is completely different," Ferguson told reporters. "I think the difference between German football and English football has been shown. In Germany you can't foul. It's foul after foul.
"The Premier League is completely different as there's physical contact in our game and it's different to Germany but, next year, he'll be better."
Kagawa has scored two goals for the Red Devils so far this campaign.