Having lost five of their last six Manchester derbies, United travel to Eastlands this afternoon with a point to prove against the Premier League champions.
It will mark Van Gaal's first taste of the rivalry since taking the Old Trafford helm in the summer, but the Dutchman says that regardless of the result, City remain firmly in the shadow of their neighbours in terms of stature.
"Abroad, we have more fans and followers on social media," he told reporters. "So it's like that.
"Also, Bayern Munich is also the biggest club of Germany. The same thing for Barcelona and Real Madrid in Spain. It takes a long time for City to reach that level."
Kickoff at the Etihad Stadium is scheduled for 1.30pm, with United currently four points behind City in the table.