UKIP MEP Steven Woolfe to stay in hospital for 48 hours
UKIP's Steven Woolfe will be kept in hospital for a further 48 hours following an altercation with a colleague in the European Parliament.
Fellow MEP Nathan Gill said Mr Woolfe would remain under observation in Strasbourg "as a precaution".
He also said Mr Woolfe had "reached out a hand of friendship" to the other MEP involved in the incident, Mike Hookem.
Officials at the Parliament have launched an inquiry into what they said were "extremely serious" events.
UKIP has launched its own internal investigation into what happened on Thursday, amid reports the two MEPs were involved in a fracas following a meeting of party representatives.
Mr Woolfe, among the favourites to be the party's next leader, later collapsed and was taken to hospital. The 49-year old had a precautionary scan which revealed there was no blood clot on his brain.
Speaking outside the hospital on Friday, Mr Gill insisted his colleague was in "good form" and there was no danger to his health "even though it was at one stage touch and go".
He said the police has not been contacted and Mr Woolfe did not want them involved.
But leader of the party in Wales, Neil Hamilton, told the BBC: "This goes far beyond need for a party inquiry. The police should investigate."
Martin Schulz, the president of the European Parliament, wished Mr Woolfe a speedy recovery but suggested the episode would have consequences for the party.
He said: "The reported facts are extremely serious," and had been referred to the Parliament's advisory committee to be dealt with "as a matter of urgency" next week.
"It goes without saying that disrespectful and violent behaviour does not have a place in the European Parliament," he added.
Interim leader Nigel Farage said he has asked the party chair and secretary to conduct an investigation early next week.
He asserted "the truth will be discovered", adding: "Other claims being made in the media by representatives of UKIP who were not even there at the time are extremely unhelpful."
UKIP sources said "a rumbustious argument" had taken place following claims Mr Woolfe had been considering defecting to the Conservative Party.
Accounts of what followed vary, with Mr Woolfe quoted in the Daily Mail as saying a punch was thrown at him.
UKIP did not deny Mr Hookem, who represents Yorkshire and North Lincolnshire, left the room with Mr Woolfe, although a spokeswoman is reported to have denied that a physical fight took place.
The BBC has been told it is believed that Mr Woolfe banged his head against a window or a wall but then got up. Following a vote two hours later "he collapsed" and doctors were called and his wife was contacted.
Speaking to the BBC's Newsnight programme, the UKIP chairman Paul Oakden said the incident appeared to be a case of "two individuals who clearly got carried away" but it would be inappropriate to speculate over what caused Mr Woolfe to fall.
Mr Oakden said the events did not characterise or define UKIP, adding: "The party is far bigger than any one individual. That's something we have demonstrated particularly over these last few months.
Mr Farage has returned as UKIP leader until a fresh election is held to find a successor to Diane James. She announced her resignation on Tuesday after just 18 days in the job, citing professional and personal reasons.
Mr Woolfe, the MEP for North West England, later announced he will run for leader in the next election, having being unable to take part in the previous contest because he missed the deadline for submitting his nomination.
Raheem Kassam, the other candidate to have declared for the UKIP leadership so far, tweeted his best wishes for Mr Woolfe.
But after news of the altercation broke, one of UKIP's major donors, Arron Banks, issued a statement in which he threatened to withdraw his support for the party, saying it was at "breaking point".
He criticised Neil Hamilton, over comments he made in television interviews where he appeared to blame Mr Woolfe for events "before anyone knew if Steven was going to be OK".
Mr Banks also warned critics of Mr Farage not to prevent Mr Woolfe - who is seen as the interim leader's preferred successor - from standing.
Mr Hamilton said Mr Woolfe was entitled to put his name forward but lashed out at Mr Banks, saying he had only "been in UKIP five minutes" and the party would be "better off" without him.