Published on Monday, 24 December 2012 16:18 Written by BBC
A BBC crew recorded a party member remarking at a meeting that Golden Dawn members had not beaten radical left MP Dimitris Stratoulis hard enough.
The party sued Mr Stratoulis when he accused them over the attack.
Contacted by the BBC, a party spokesperson dismissed the remarks at the meeting as a "joke".
Greek police spokesman Lt Col Christos Manouras told the BBC on Monday that as soon as police heard the BBC broadcast, they recorded the clip of the Golden Dawn meeting and sent it to the office investigating the alleged attack on Mr Stratoulis.
The MP from the Syriza bloc was reportedly attacked after a football match in the Olympic Stadium on 16 December by three men who, he says, threatened to kill him. He is said to have suffered light injuries.
Golden Dawn is one of the most right-wing parties in Europe and its anti-immigrant language and logo, redolent of a swastika, underline why many call it neo-Nazi, the BBC's Tim Franks reports from Athens.
A recent opinion poll suggests the party's support has grown since the last election, when it won 18 seats in parliament.
Golden Dawn denies involvement in violence.