The European Parliament launched a disciplinary inquiry on Friday into a scuffle between members of the UK Independence Party that left one British MEP in hospital with a head injury.
Martin Schulz, the speaker of the EU legislature, wished UKIP leadership hopeful Steven Woolfe a swift recovery.
“The reported facts are extremely serious,” he added in a statement.
“It goes without saying that disrespectful and violent behaviour does not have a place in the European Parliament.”
Schulz, a German Social Democrat who has had a combative relationship with the eurosceptic party that helped persuade Britons in June to leave the EU, asked the disciplinary panel to deal with the matter “as a matter of urgency next week”.
He said the incident, details of which are unclear, could constitute a breach of parliamentary rules. He cited rules that refer in part to members acting with “respect for Parliament’s reputation”, showing “mutual respect” and ensuring they do not “disturb the peace and quiet of any of Parliament’s premises”.
A breach can be penalised by a reprimand, loss of voting rights or parliamentary office and a fine worth two to 10 days of subsistence allowance, or from 612 ($682) to 3,060 euros.
The panel advising Schulz comprises a Czech Communist chairman and four other EU lawmakers, none from UKIP but including one Briton, from the ruling Conservative party.
UKIP leader Nigel Farage, who stepped in when his elected successor stepped down on Wednesday amid furious faction-fighting in the party since the referendum, has launched an internal inquiry into the incident and has refused to say who was responsible.
Woolfe, 49, is being kept in a Strasbourg hospital for a further two days for observation, UKIPofficials said on Friday.
He told the Daily Mail that UKIP defence spokesman Mike Hookem “landed a blow” as they stepped out of a heated meeting with fellow MEPs. An aide to Hookem, 62, a former army commando, denied that, telling British media via an aide, that he did not touch Woolfe and that it was a purely “verbal altercation”.