Loew had said back in March he wanted only the fittest players on his squad for the tournament in Brazil where they will face a hot and humid climate made worse by the earlier kickoff times and the long travel distances between matches.
Germany have been drawn in Group G along with the United States, Ghana and Portugal at the tournament starting in June.
"At the moment we have only seven or eight players who are in top form," Loew told Stern magazine on Wednesday. "This whole situation is causing some headache.
"Klose, (Sami) Khedira, (Mario) Gomez, (Ilkay) Guendogan, Schweinsteiger, they are all players who are pillars in our team but they lack match rhythm," he said.
Holding midfielder Khedira is only just back from a cruciate ligament tear last year while midfielder Guendogan is unlikely to make the cut given he has not played since August last year due to a back injury.
Bayern's Schweinsteiger missed much of the season with a string of injuries just like forward Gomez who has hardly featured for Fiorentina this season.
Add to those injured Borussia Dortmund's Sven Bender as well as Schalke 04's Benedikt Hoewedes who is hoping to come back on Saturday after weeks out injured and Hamburg SV's Marcell Jansen, then choices for Loew become even more limited.
Mesut Ozil is also only just back from injury after a mediocre season at Arsenal as is Dortmund defender Marcel Schmelzer while Bayern Munich's Toni Kroos and Jerome Boateng are going through a slump in form since their club won the league title in March.
Germany are looking to end an 18-year title drought and Loew said he was eager to satisfy that demand but warned they were not the only ones after the trophy.
"We have our chances to win the title but other teams have equally big chances but this is something no one wants to hear at the moment," he added.
"As a coach you are always with your back to the wall. If you win then you are celebrated like a Messiah for the whole people but when you lose a game then you are public enemy number one."
- Sports & Recreation
- Bastian Schweinsteiger
- Miroslav Klose