Coach Joachim Loew has admitted having concerns about Germany's form ahead of Wednesday's friendly against Chile with the Brazil 2014 World Cup just over 100 days away.
"On paper, we have a top team, but the reality is at the moment a bit different," said Loew, whose side won nine and drew one of their 10 qualifiers.
"Several players have been injured for months, while others have struggled with a lack of rhythm or form.
"The door is still open. We need players at the World Cup who are our current best, not just theoretically so."
Loew will announce up to 28 names on May 8 which will be trimmed to the final 23-man World Cup squad after the Germans' training camp in South Tirol, north Italy, from May 21-31 before the tournament starts on June 12.
"It will all depend on the fitness and form of our World Cup candidates and whether some players are involved in the Champions League final in Lisbon on May 24," explained Loew.
The Germans will also take the Under-20 squad into Tirolean camp to hold regular practice matches against the junior squad, who will mimic the playing styles of Germany's World Cup group opponents Portugal, Ghana and the United States.
Germany host Chile in Stuttgart in the only friendly before the May 8 announcement.
Four uncapped players having been called up including Sampdoria centre-back Shkodran Mustafi, Ausburg midfielder Andre Hahn, Hamburg striker Pierre-Michel Lasogga and Freiburg centre-back Matthias Ginter.
Bayer Leverkusen midfielder Lars Bender has dropped out with a dead leg, while Loew hopes veteran striker Miroslav Klose will start: "he is optimistic he can play".
The 35-year-old is set to become Germany's top scorer of all time having equalled Gerd Mueller's record of 68 goals in the white shirt, but he sat out Lazio's 1-0 Serie A win against Fiorentina on Sunday with a strained abdominal muscle.
Captain Philipp Lahm will be moved from right-back to defensive midfield alongside Bayern Munich team-mate Bastian Schweinsteiger, who will play his first friendly since August 2011.
"A fit Bastian Schweinsteiger is enormously important for his experience, his influence and his leadership qualities," said Loew.
The 54-year-old has said he is expecting to learn "some truths and get some clarity" from the Chile friendly.
"The clock is ticking, only those who hear it and feel the pressure to perform will have a fighting chance of a place," said Loew.
"I appeal to any candidates to make their CV as good as it has to be if one has big goals."
Loew's main World Cup injury concern is defensive midfielder Sami Khedira, who is tipped to return soon by his Real Madrid boss Carlo Ancelotti, while Bayern Munich centre-back has only an outside chance to be fit after knee surgery.