It is thought the injured researcher trapped in the 1,000 metre-deep Riesending cave in southern Germany may be rescued by the end of this week.
Over 100 emergency workers have struggled to rescue the injured man who became trapped in the cave after a rock fall.
Johann Westhauser, 52, was one of the researchers to discover Riesending, which is Germany's deepest cave system.
The system, which a rescue official has described as one of Europe's most difficult, extends over 19.2km and lies in the country's south-eastern corner.
Mr Westhauser suffered injuries to his head and chest in a rock fall in the cave on Sunday.
He cannot climb to the surface on his own as the ascent involves steep shafts and narrow tunnels.
A rescue team has reached the cave explorer, however it is believed it could take days to bring him to safety.
Earlier this week, Roland Ampenberger of the Bavaria mountain rescue service, said: "The issue for us is how to get him out... there is a permanent danger of rocks falling which is why the operation is so complicated."
Telephone lines have been laid several hundred metres deep to help the rescue effort, while others have set up camps within the cave system.
An Austrian mountain rescue team has arrived at the scene, while a third Italian team, including a doctor, are also reported to be making their way there.
The cave, located near Bavaria's border with Austria, is 1,148m deep.
It took one of the man’s companions 12 hours to climb out and call for help.
The other stayed with the researcher until the first rescue teams arrived.
"He is responsive but he is not well”, German media quoted a rescue official as saying.
Rescue teams initially expected it would take weeks to recover the man from the cave as he could not stand.
Local media have since said the speleologist is now responsive and able to stand up for short periods of time, so the rescue may be completed by the end of the week.
