The preliminary proceedings were confirmed to Westfälische Nachrichten and it comes after German television channel RTL broadcast footage of Beerbaum allegedly using the practice of parallel bars - related to "poling" - which is illegal in Germany and under the rules of the International Equestrian Federation.

Parallel bars are intended to encourage horses to pull their legs up and jump higher.

To achieve this, an obstacle bar is lifted up so that it hits the horse's legs while they are clearing a jump.

This technique is forbidden as it can often cause the animal pain.

An investigative journalist worked on the project for two years, disguising themselves as an intern to gain access to Beerbaum's training methods.

The 58-year-old said he plans to take legal action against the broadcaster of the report, claiming the video had "nothing to do with parallel bars" and was instead showing "touching", a method permitted under German law.

Beerbaum added that the object used met the touching requirements set by the German Equestrian Federation (FN).

"The contribution of RTL is demonstrably false, defamatory and in many ways slanderous," said Beerbaum.

"Of course we will take legal action against this. 

"It is unacceptable that secret recordings were made on my private property.

"With regard to the accusations against me and my team: the well-being of the horses is a top priority for me and my team. 

"Only a horse that is properly treated, professionally cared for and fed, trained and managed can perform in sport. 

"The horses are our capital that we take care of day in and day out."

FN secretary general Soenke Lauterbach claimed that these allegations are being taken seriously by the organisation when they first emerged, and an investigation was launched.

"This is precisely why we will carefully analyse the footage broadcast on Tuesday evening and then draw appropriate conclusions on how to proceed," Lauterbach said.

"In order to be able to make a serious assessment of the facts, all video and evidence material is required, we therefore call on RTL again to make this available to us in full.

"Even now, regardless of the contribution shown, we can clearly say that the use of square bars and dimpled or spiked bar material is unacceptable and not in accordance with the principles of fair equestrian sport."

People for the Ethical Treatment of Animals (PETA) had said it would file criminal charges against Beerbaum and others involved in the videos, while the FEI is also investigating.

Beerbaum was the individual jumping gold medallist at the Barcelona 1992 Olympics, adding team golds with Germany at Seoul 1988, Atlanta 1996 and Sydney 2000.