The 21-year-old has partnered Nemanja Vidic at the heart of United's defence in recent weeks, as Red Devils skipper Ferdinand battles to shrug off a calf strain.
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Many pundits were surprised with Ferguson's decision to plunge the ex-Maidstone United player in at the deep end, with the former Fulham star still learning his trade at the highest level, having only made the move into professional football two years ago.
But Smalling's rapid rise to stardom comes as no surprise to the Old Trafford supremo, who feels his England Under-21 international will only get better with experience.
“We are very pleased with his performances”, Ferguson told Inside United. "It's an outstanding contribution he has made. But, do you know, I expected him to do well. I had no doubts about him.
"He's done really well for us and he is improving all the time. He is developing all aspects of his game because he wants to learn and improve. He likes defending, he enjoys it. So he's a real bonus.
"We started him against [Manchester] City with Rio being out and it's not easy coming in for your first derby at 21 years of age, having only been with us nine months. But I thought he would do well."
And Ferguson believes Smalling and Jonny Evans could prove to be the bedrock of United's defence in the future.
"They're young, but Evans for example has already played a lot of games for us. He played almost three quarters of the matches last season. His time will come."
By Matt Maltby
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