The attack occurred on Sunday morning as, Bernhard Günther, chief financial officer with Essen-based company Innogy, was on his way to a bakery.

As he was a walking through a park in the town of Haan at around 9am, two men approached him and threw a liquid at him. The substance immediately reacted with his skin and caused serious injury.

Günther was able to run back to his home, from where he was taken to hospital for treatment. Initially the injuries were so severe that doctors described his situation as critical. But by the afternoon he was no longer considered to be in a life threatening situation.

An investigation into attempted murder has been opened. The attackers were not masked at the time of the incident and police say they possibly said something to their victim as they attacked him.

While police have not confirmed what the liquid was, they say they are working on the assumption that it was an acid.

“We are deeply shocked. News of the attack has affected us all,” Innogy CEO Uwe Tigges said. Innogy is a subsidiary of energy giant RWE.

“We are thinking of Bernhard and his family and hope that he recovers quickly,” he added.

Police have said that they cannot yet say anything about a possible motive and are “investigating in every direction.”

The Bild daily reported that the domestic security service, which is responsible for politically motivated crime, was investigating.

RWE has long been engaged in a battle with environmental protesters over its open-pit coal mining operations, including at the flashpoint forest site Hambacher Forst where activists have lived in a protest camp for years.