Unfancied Switzerland caused a major upset by beating then World Cup tournament favourite Spain in their opening game, and face Group H co-leaders Chile in their next game.
"We have to play with a cool head and not give Chile chances. If we lose our heads, we don't stand a chance," Hitzfeld told a news conference at the team base camp in Vanderbijlpark, about 90km from Johannesburg.
"Mentally, the game against Chile will be more difficult than our first game," the German-born trainer said before the team departed for Port Elizabeth.
However, Hitzfeld said it was not certain that Switzerland's top striker Frei, would start in the game.
"The fact that he (Frei) trained with the team does not mean he is going to start against Chile," Hitzfeld said.
"I will only decide on the day of the match, however I am happy I have an additional attacking option," he added.
