21-year old Depay, Fer's teammate in the Holland national team, will arrive at Old Trafford in the summer in a £25million move from PSV Eindhoven.
Fer said: "I have known him two or three years now with the national team and he asked me what the Premier League is like.
"I told him it's a hard league, but for him, with his ability and skills, I think he can play a massive part for United.
"Playing with stars like (Wayne) Rooney and (Angel) Di Maria will be great for him and will make him better for sure.
"Of course, he has two teammates from the national team there already in (Robin) van Persie and Daley Blind so that will help.
"He knows Louis van Gaal too and he will make him a better player as well."