Wednesday's game between Darmstadt and Kaiserslautern was abandoned at half-time after Kaiserslautern coach Jeff Strasser required treatment in the dressing room.
The former Luxembourg international was taken to hospital for checks, Kaiserslautern said, but gave no details of his condition.
Kicker reported the 43-year-old was conscious.
"We send our best wishes to Kaiserslautern and wish Jeff Strasser all the best on the road to recovery," Darmstadt president Rudiger Fritsch said. "On days like today, we are all reminded once again that there are more important things than football."
The game was still goalless when it was stopped.