The Japan star became the first Asian player to score a treble in the Barclays Premier League as he launched United towards a 4-0 win over Norwich at Old Trafford.
It was the stand-out contribution to what was largely a drab affair - albeit one that was lit up by Wayne Rooney's late wonder goal - and enough to take United 15 points clear of Manchester City in the title race.
Ferguson feels there is much more to come from Kagawa, whose only other goals this term came prior to a knee injury sustained against Braga in October that kept him out for over two months and hampered progress following a summer move from Borussia Dortmund.
"It was a brilliant day for him," said Ferguson. "He is a good finisher. His second goal was composed and intelligent, his last was brilliant.
"He missed that period of football in October and November that set him back a bit. He is gradually getting his form back but next year he will be far better, you will see a really good player then."
Strangely, Kagawa's heroics may not be enough to get him a starting berth against Real Madrid on Tuesday.
Rio Ferdinand and Rafael were left out with that game in mind, while Ryan Giggs was also denied a 1,000th senior appearance in readiness for some meaningful contribution against Jose Mourinho's men.
"It will be a fantastic night," said Ferguson. "You are talking about two of the greatest clubs in the world.
"Emotions will be high and I am sure it will be a tremendous match. If we can get a blank against us on Tuesday we would go through. But I think both teams will score. I just hope we get more than them."