Los Che are currently at the top of the La Liga table on goal difference thanks to four wins and draw from their first five matches.
Despite putting together such a strong run during the past few weeks, Mustafi has warned his teammates that they must not let it go to their heads.
"It's always important to be on the top of the league but the most important thing is to stay calm because it is very easy to fall," the summer signing is quoted as saying by Marca. "The difficult thing is to stay there and we cannot let it go to our heads. We should be careful."
Valencia can continue their unbeaten start to the season on Sunday when they travel to Real Sociedad.