The Black Stars, who lost their opening match to the USA, will be all but out of the tournament if they are beaten by the Group G leaders.
Despite Germany's status as favourites to win the game following their resounding 4-0 victory over Portugal, Gyan believes that Ghana could cause an upset.
"We need to sit down, take a long hard look at our errors and work hard," the 28-year-old striker told FIFA.com. "We have to regain our focus and not let nerves get the better of us.
"It's going to be a difficult match but we need to stick together more than ever and play our game. I can't say what's going to happen but football always throws up a lot of surprises."
Gyan has scored 40 goals in 79 appearances for Ghana since he made his debut in 2003.