The 17-year-old midfielder played 90 minutes of Borussia Dortmund's 2-1 defeat in the first leg of their Champions League quarter-final tie on Tuesday.
The youngster put in an impressive performance but it was not enough to stop City from taking an advantage into the second leg with Phil Foden scoring a 90th minute winner.
"Honestly, I'm knackered now!" he told BT Sport after the game.
"They're brilliant, I think they're one of the best teams in the world if not the best.
"The way they move the ball and the way they go to regain the ball after they lose it is world class.
"You give De Bruyne that much time in the box then he's going to score and you give him that much time around the box then he's going to put a ball in that damages is and it did."
When asked about the bleeding knee he was nursing after the game, the midfielder replied: "That's from chasing them around!"