The midfielder scored twice for the 3-1 fifth round victory.
Guardiola said, "He’s not a typical player from the Academy because they are all small and have big talent but he has a big, big presence.
“Sometimes we take a good decision otherwise he would not have scored two goals today.
“Normally he’s an attacking midfielder and runs to the box really well.
“He adapted really well to the full-back role.
“Nico’s another threat from set-pieces because we are not a tall team.
“He helps us and played really good with the ball, without the ball.
“Two fantastic goals.”
Guardiola also stated: “I don’t take for granted the difficulty when you play an incredibly organised team. I’m not surprised what they did against Liverpool.
“It was difficult to challenge them because they are incredibly organised defensively.
“I don’t take for granted how good we have done many, many things. Every step is getting better. Many good things happened.
“Jack (Grealish) played really good. Vitor (Reis) played really good. All of them. Nico. We had a lot of possession with patience because they want to make transitions.
“Really pleased for the performance.
“We have been many years in the quarter-finals and we’ll see the draw tomorrow.”