Fernandes has made an immediate impact at Old Trafford after signing from Sporting Lisbon in January, scoring four goals in 12 appearances in all competitions.
"I've followed him for a long time because I played in the Portuguese league at Benfica," Matic told Sky Sports.
"I knew he would bring quality for us. He played for a big club with a lot of pressure to win, but I didn't think he would adapt so quick. From the first minute in the Premier League he made the difference.
"I'm happy for him and happy we have him in the team.
"He's playing in the position where he needs to make the difference. He has all the ability to be the leader on the pitch."