The 23-year-old former Borussia Dortmund midfielder, currently in China with the rest of the United squad, has already impressed his new team-mates.
Ferdinand said: "I've been very, very impressed. I'd seen him play for Dortmund on TV and I looked on YouTube.
"He's been fantastic. He's quick, he's sharp, he has great awareness, he plays off both feet. I'm excited about playing with him and getting the season started.
"He's been one of the better players in Germany for the last few years. I think he will bring that form to Manchester United. I think he'll be a great acquisition."
Kagawa arrived at Old Trafford on a four-year deal last month and has taken little time to adapt to his new surroundings.
Manager Sir Alex Ferguson has been delighted with how quickly he has got to grips with life at his new club despite not yet having a grasp of English.
The Scot told a press conference in Shanghai: "The thing that's quite impressed me is that every exercise we do on the training ground, he's never needed it to be explained.
"After one demonstration, he joins in as if he's known the language forever. Of course, we know he doesn't speak the language, but it isn't a problem.
"It just goes to show that a good footballer can pick up exactly what's needed. He's been fantastic in that respect. I've been quite surprised at that."
Kagawa and his team-mates will play their latest pre-season friendly on Wednesday when they take on Shanghai Shenhua, the latest destination for Nicolas Anelka and Didier Drogba.
The Chinese game is proving a lucrative market for big-name players approaching the end of their careers, although England defender Ferdinand has insisted it is not yet on his horizon.
He said: "I think when you get to my age, if you look too far ahead, your legs can get taken beneath you.
"All I'm interested in is playing for United. It's what I enjoy.
"Pre-season began well. I'm just thinking about this season and playing for Manchester United. I'm obviously very happy here and not looking at going anywhere else."
Meanwhile, Ferguson admitted finding a long-term replacement for 37-year-old midfielder Paul Scholes, who came out of retirement last season to star for United once again, is an ongoing concern with illness preventing Darren Fletcher from staking his own claim.
Ferguson said: "Darren has a medical situation that he's trying hard to keep under control. We don't expect him back immediately, but hopefully he does come back at some point.
"Paul Scholes a year ago was coaching my reserves - now he's back playing, and everybody attached to United is delighted. He's such a fantastic player.
"In the long-term, trying to replace Scholes is very difficult. To replace a great player like him would be hard for anyone."
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