Ballack ankle too swollen for scan
Ballack limped off during the first half of Chelsea's 1-0 FA Cup final win over Portsmouth on Saturday after a late tackle by Kevin-Prince Boateng.
An X-ray at the stadium showed he had not broken any bones but the 33-year-old, who has 98 caps, said he was still worried.
"The swelling is so strong that the examination will be done on Monday instead of Sunday as originally planned," said the DFB in a statement.
Germany coach Joachim Low, whose squad is training in Sicily before next month's World Cup, added: "We received the news with great concern.
"The good news is that nothing is broken.
"Naturally, we hope that the injury is proven to be not so serious. Michael is our captain and absolute leading player."
Germany face Australia, Serbia and Ghana in Group D at the World Cup.