Terry played with De Bruyne at Chelsea.
"He was a young boy, didn't really get his chance at Chelsea," Terry said of the Belgian on Sky Sports.
"You couldn't judge him on four or five games playing here and there.
"What he's doing today in the Premier League, if he plays like that for four or five years, he's going to be with the greats.
"When you're a younger player, you can't set the world alight in the last group game in the Champions League when you've already qualified.
"Sometimes you need to go away. I did it when I was younger. I went away and got a bit of game time, grew up a little bit and came back a better player. That's what you have to do at these top clubs."