The seriously injured 52-year-old was still awaiting rescue on Monday, 1,000 metres underground in the Riesending caves in southern Germany.
On Monday, emergency services managed to make contact with him in the cave near Berchtesgaden, but police said the man was not able to be moved. A specialist rescue team has been called in from Switzerland.
The researcher from Stuttgart, who was one of the first to discover the cave years ago, was exploring Germany's deepest and longest cave with two companions on Sunday when he was injured by the rock fall at around 1.30am.
The man suffered injuries to his head and upper body. One of his companions managed to climb up the cave and raise the alarm, while the second stayed with the injured man. It took the guide almost 12 hours to get to the surface.
Around 200 rescuers are now involved in the operation to get him out.