The £12m summer signing has started just 14 times in his first Premier League season, and a knee injury suffered in the autumn kept him out for two months.
But amid a stop-start campaign Kagawa has managed a hat-trick against Norwich, and his two assists at West Ham in midweek took United a point closer to their 20th English title.
Ferguson said: "He's doing very well for us now. He has fantastic composure on the ball and his decision-making is good.
"He seems to always pick the more sensible pass and for the first goal at West Ham he had the composure to take the player on in a tight area and roll the ball to Antonio Valencia for a tap-in."