Kagawa has made 16 appearances for United since his move from Borussia Dortmund last summer and missed two months earlier in the season due to a knee injury.
He was entrusted with a starting role in last week's UEFA Champions League tie with Real Madrid and Ferguson was pleased with the Japan international's display in the 1-1 draw.
The United boss is also confident that Kagawa will have a greater impact in the Premier League once the 23-year-old has become more accustomed to the physical demands of English football.
"The difference in German and English football is that in Germany you can't foul," said Ferguson.
"It's just foul after foul and you're not allowed to touch anyone in Germany so he's come from that environment to the Premier League which is totally different.
"There's a physicality to our game which is different from Germany but next year he'll be better.
"In the first half-hour against Madrid he was terrific and he was making some great runs through them. We thought that was going to be one of our biggest assets in the game.
"If people don't see that, it's actually unfair, but he did really well for us in the first half."