Pep Guardiola's side have scored nine goals without reply in the past week and will provide Watford with the sternest test so far of their own unbeaten record.
Watford would go top of the Premier League table with a victory, but Silva is not getting ahead of himself.
"We are happy with everything we did until now, we have got important points for our fight but nothing more," he said.
"It's important to be unbeaten. We had good performances in some of the matches as well and we need to continue to work hard to win in the right way.
"Is this our biggest test? No. It's one more game, against a great, great team.
"We have started well and got an important eight points but we need to know our goal. We need to understand our position and not look at different things because we started very well. It's important not to lose our focus.
"We will not change our goal because we got important points and we started well.
"It's clear to us what we want to do, to keep our club as a Premier League club and to try to do something better than the last two seasons.
"That is our goal for the season and I believe we can do it, but we need to improve every day in training and fight to take points from every match."