Germany coach Joachim Loew says his team are yet to hit peak form in the World Cup despite their unbeaten run to the tournament's quarterfinals.

Germany won their first match against Portugal 4-0 but have since drawn with Ghana and eked out narrow wins over the United States and Algeria.

Speaking on the eve of his team's quarterfinal clash with France at Rio's Maracana Stadium, Loew said he was still striving to find the best formula for his side.

"We have not yet delivered our best possible performance," Loew said. "But I don't think anyone has reached their absolute top performance yet.

"It's not a computer game that is easily figured out. You can't easily figure out your opponent and it's not easy to program your own team. Mistakes are made. And then there are other elements from beyond the pitch."

Among those elements is a flu epidemic that has swept through his squad.

At least seven players have been affected by the bug, including defender Mats Hummels, who was reportedly bed-ridden for three days.

"One third of our squad has been complaining about a sore throat," Loew said. "But Wednesday and Thursday all players have been training and none were feeling exhaustion. I just hope that stays stable until Friday."