Evian-les-Bains - With fitness worries over central defender Jerome Boateng, Germany coach Joachim Loew gave his players the day off on Thursday.
The World Cup champions need to get through four more matches to claim their fourth European Championship title - and first since 1996. It starts with the round of 16 game against Slovakia in Lille on Sunday (June 26).
Boateng is bidding to overcome the calf muscle problem that forced his early substitution in the 1-0 win over Northern Ireland on Tuesday.
"The medical team and Jerome are working hard on it. We're all very positive about it and hope it works out. We'll do everything to make sure (he's fit)," Germany assistant coach Marcus Sorg said Thursday at the team's tournament base.
Sorg was unable to say for sure whether the 27-year-old defender, arguably Germany's player of the tournament so far, will be fit by Sunday.
"I'm not a prophet," Sorg said.
If Boateng doesn't make it, Benedikt Hoewedes or Shkodran Mustafi will likely partner Mats Hummels in front of goalkeeper Manuel Neuer.
"We have perhaps two of the best three central defenders in the world in Mats and Jerome. But we've a lot of trust in the guys behind them, in Beni (Hoewedes) and Musti (Mustafi)," assistant coach Thomas Schneider said. "We trust the players that come off the bench."
Slovakia defeated Germany 3-1 in a tournament warm-up game in Augsburg on May 29, thanks to goals from Marek Hamsik, Michal Duris and Juraj Kucka.
However, Germany was missing first team regulars Neuer, Hummels, Toni Kroos, Thomas Mueller and Mesut Ozil, and a powerful storm interrupted play for 40 minutes and conditions were difficult on the water-logged field for the second half.
"We can't take the friendly game as an indicator," Schneider said. "We know that Slovakia asked a few questions at the time but we were in preparation mode. Now we're in the knockout rounds. There are different factors at play."
Slovakia finished third in Group B behind Wales and England, its 2-1 win over Russia in Lille proving crucial to its progression before it sealed the deal in the scoreless draw with England.
"They're a technical side, very direct and compact, and they've shown their defensive side already in the tournament," Schneider said. "For us it's a hard task but a task we can manage and one we definitely will."
Loew, who had earlier said his side knew what to expect against Slovakia, warned against any complacency.
"We want to stay as long as possible in France. The smallest mistakes now decide whether we go home or reach the next round," said Loew, who gave his players their second day off in the tournament to stay fresh and recover from their travels.
Germany's team base is about 500 kilometres from Paris and more than 600 from Lille, cities where the side played all its group games.
If Germany defeats Slovakia on its return to Lille, the team will play either Spain or Italy in Bordeaux, where progression would mean a semi-final match in Marseille. The final is back at Stade de France near Paris.
"All the concentration is on the next game and then we'll see what happens afterward," Schneider said. "It's not bad that Italy are playing Spain as one top team will be out. In the end you have to beat every team if you want to be European champion."