City will face the Bundesliga side in the quarterfinals following the draw on Friday and Haaland, who has been linked with a move to the Etihad Stadium, will pose a significant threat after scoring 31 goals in 30 games this season.
“The numbers speak for themselves,” Guardiola told a news conference on Friday. “He is one of the best strikers in the world at his age. The numbers are impressive.
“I know the quality of him and I think everyone knows, but in two weeks I will answer better because I didn’t see much.
“Dortmund is tough but all of them would have been. We have to discover how they are as a team, do a good first game and then the second one.
“The best team will go through, no more secrets. We have two weeks to analyse their games, how they do and that’s all.”
City are looking for a striker this summer and Haaland is one of the names in the frame, although Dortmund expect to keep the 20-year-old for at least one more season.
Haaland’s father, Alf-Inge, played for City between 2000 and 2003 but Guardiola refused to be drawn on whether Erling will follow.
“I don’t like it when people talk about our players. You understand I cannot answer this question.”