A German far-right politician suspended by Alternative für Deutschland (AfD) is under investigation by authorities after sending a party colleague to hospital with a “friendly” punch to the torso.

Andreas Kalbitz, a former neo-Nazi who is fighting for his party membership in the courts, reportedly ruptured the spleen of his temporary replacement in the Brandenburg state parliament, Dennis Hohloch, in an incident on 10 August.

“Of course I very much regret this incident and this chain of unfortunate circumstances,” Kalbitz told Berliner Zeitung, seeking to quash rumours of a violent altercation between the two men.

The news magazine Der Spiegel quoted a text message from one of Kalbitz’s political allies dismissing reports of a disagreement as a “fairytale” and saying Kalbitz had merely given his colleague a “friendly bop to the sides”.

The state prosecutor in Potsdam said on Tuesday it was investigating the incident on suspicion of bodily injury caused by negligence.

Kalbitz, a former paratrooper who ran for premier of the state of Brandenburg last year, is seen as an influential figure in the AfD’s eastern branches but has proved increasingly divisive in a party that tries to attract both “moderate” middle-class libertarians and rabble-rousing nativists.

In May, Kalbitz was ousted for allegedly declining to inform the party of his former membership of a banned neo-Nazi group, German Youths Loyal to the Fatherland, when applying to join the party in 2013.

Last year he was revealed to have been named by the German embassy in Athens as one of 14 neo-Nazis who travelled to the Greek capital in 2007 for a far-right rally.

His colleague Hohloch is standing in as head of the AfD’s parliamentarians in Brandenburg while Kalbitz tries to restore his party membership through legal channels.

On Tuesday afternoon, AfD politician Kai Laubach posted an open letter on Facebook in which he alleged that Kalbitz had also punched a party colleague called “Kevin” at a party congress in 2019, and that he was referring to Hohloch as a “fragile wuss” behind his back.