City will be looking to take advantage of their first leg lead and progress to the next round, with the hope of clinching Europe's most prestigious prize, one that Guardiola is desperate to win and has not claimed since 2010-11.
"It's all very open. When you play a side like Madrid, nothing is ever certain," the Portuguese told AS.
"We've seen a lot of ties in the last few years get turned around. Look at Barcelona last year, beating Liverpool 3-0 and then losing 4-0. You never know.
"You can't write any team off, much less Madrid who have won 13 European Cups. No one else has the experience Madrid's players have in this competition, so we can't think we've already beaten them."
Silva has been heavily involved in the recent success at the Etihad Stadium and has continued to impress with seven goals and eight assists in all competitions so far this campaign. body check tags ::