Ronaldo scored twice on his second debut at Old Trafford, as United saw off Newcastle 4-1 on Saturday.
Speaking on his Vibe with FIVE YouTube show, Ferdinand explained: “He can jump, but again it’s about positioning of where he’s going to be to receive the ball.
“That’s one thing that I would say, not a criticism, but one thing to look at and learn from, from Man United’s point of view from the weekend’s first game.
“And I’m telling you, he’d have been in there [the dressing room] after and this week saying, ‘Listen, cross that ball! When you get opportunities to cross the ball, you put it in there because I’m aggressive and I want the ball.’
“And he knows, and it’s well documented that I’ve always said this for the last few years, the defenders in this country are not great at defending crosses. It’s not an art that is actually honed anymore.
“Because when I see balls come in the box at the moment, body positions and angles etcetera are way off. And it isn’t easy as a defender, I can tell you I’ve made many mistakes in that position. But you’ve got to work at it.