The 22-year-old has been in a coma since his car collided head-on with a truck on September 28. He sustained serious head injuries and needed emergency surgery.
"So-called low blood sugar seems to have been the cause for the driver to drift into oncoming traffic and crash with the 40-tonne truck," Heidelberg police and the state prosecutor's office said in a joint statement.
Doctors have said the condition of the former Germany Under-21 player remains critical but he has shown some signs of stabilising.
