Ferguson uses his column in the Newcastle edition of United Review - the Reds' official match programme - to wax lyrical about the 22-year-old's maturity and the progress he has made, particularly in the last 12 months.
"The truly eye-catching improvement this season so far for me is the maturity that young Rafa has added to his game," says the United boss.
"He has always shown himself as a defender with ability and great enthusiasm, but not always with great decision making, especially in European football, giving him - and us - some scary moments.
"His performance against Queens Park Rangers [last month] was outstanding with his defensive work and attacking making his presence a key factor in our 3-1 win.
"I would have no hesitation saying that he is our most improved player this season with a couple of goals a reflection of his eagerness to lend a hand up front."