Ferdinand followed Kagawa's progress at Borussia Dortmund and was particularly impressed by his performance in Dortmund's destruction of Bayern Munich in the German Cup final in May.
The defender will begin training with his new colleague in the coming days and he is backing him to achieve big things at Old Trafford.
"I can't wait to see Kagawa in action," Rio told MUTV at Nike's 'The Chance' event. "I watched him on TV last season and saw him in the cup final when Dortmund beat Bayern Munich and he looked very impressive.
"I think a lot of people will be surprised by how good he really is and hopefully he can hit the ground running."
Ferdinand joined a number of his team-mates at Carrington earlier today as the players - bar the Euro 2012 contingent - returned to training after a seven-week break.
Rio insists he's delighted to be back and is gearing up for another exciting pre-season tour - delivered to the world by DHL - which will see the Reds play games in South Africa, China and Europe.
"I love pre-season," he declared. "This is the longest time I've had off and I'm raring to go. Even the family at home have been trying to get me out of the door to come to training! I've been getting cold feet in the house sitting around doing nothing. It's hard work but I love it.
"I can't wait to see the fans in all the different countries we're visiting on tour," he added. "It's great to see so many different parts of the world.