Germany will be without Thomas Müller and Antonio Rüdiger in tomorrow's friendly against Oman as the duo continue their recovery from injury.
The same goes for Antonio Rüdiger, who is also working his way back from an injury.
Germany will also be without Marc-André ter Stegen, who is sidelined with a stomach bug.
"It may well be that we rest one or two players tomorrow. Thomas Müller and Antonio Rüdiger will return to team training first thing on Saturday," Flick said at a press conference ahead of the Oman game.
"As soon as Marc-André ter Stegen can travel, he will. He’s on the road to recovery."
Müller last featured in a Bundesliga game at the end of September and has missed Bayern's last seven league games due to various issues, most recently a hip injury.
Nevertheless, Flick insists the 33-year-old is in a good condition for the World Cup.
"He's had a long break, but he has been training well recently. His rehabilitation at Bayern Munich was very good so we've been able to continue his training programme," Flick told reporters at a press conference today ahead of tomorrow's friendly against Oman, which will see Müller and Antonio Rüdiger
Even so, there is no guarantee that Müller will start against Japan.
"We have a lot of quality across the front line, which is something we need if we want to be successful during the tournament. If the players are putting in their best performances, then it will be extremely difficult for us to decide who to pick.