Chester resident Steven Woolfe MEP has collapsed at the European Parliament building in Strasbourg amid reports he was punched by a colleague.
The alleged incident comes just a day after Mr Woolfe announced he was seeking election as leader of the UK Independence Party for a second time.
He is described as being in a 'serious condition' in hospital at the French city.
UKIP was claiming Mr Woolfe had been taken ill but acting leader Nigel Farage has now issued a statement about the altercation.
He said: "I deeply regret that following an altercation that took place at a meeting of UKIP MEPs this morning that Steven Woolfe subsequently collapsed and was taken to hospital. His condition is serious."
Mr Woolfe, who lives near Chester city centre with his wife Fiona and young daughter, was today supposed to be enjoying his 49th birthday during a working day at the parliament.
A statement issued by Team UKIP on Twitter just after midday said: “UKIP spokesman Steven Woolfe MEP was taken suddenly ill in the European Parliament building in Strasbourg this morning. He has been taken to hospital in the city and he is undergoing tests.”
Mr Woolfe was ruled out of the previous leadership contest after missing the nominations deadline but the eventual winner Diane James then unexpectedly quit the job after just 18 days, triggering a fresh election.
The Euro MP yesterday declared his candidacy in the leadership election and was being touted as the front-runner with backing from UKIP’s biggest donor Arron Banks and Mr Farage, who is acting as interim leader.
Interestingly, Mr Woolfe, who felt let down by his party’s National Executive Committee for refusing to allow leniency when he missed the nominations deadline due to computer problems, has revealed he considered joining the Conservative Party under Theresa May’s leadership.
He said in a statement yesterday: “In the last few weeks I have thought long and hard about my political future and how I can best help build the Brexit Britain we voted for in June - a meritocratic, independent and prosperous country that stands up for the millions of people who have been ignored for too long.
“I have been enthused by the start to Theresa May’s premiership. Her support of new grammar schools, her words on social mobility and the growing evidence that she is committed to a clean Brexit prompted me, as it did many of my friends and colleagues, to wonder whether our future was within her new Conservative Party.
“However, having watched the Prime Minister’s speech on Sunday I came to the conclusion that only a strong UKIP can guarantee Brexit is delivered in full and only our party can stand up for the communities of the Midlands and the north.
“We can replace Labour as the main opposition party. We can build on our remarkable achievements, stand up for the ignored working class and secure a radically different political landscape in Britain for a generation. Under my leadership, that is what we will do.”
Mr Woolfe has talents in other areas having played semi-professional football in his youth and has a half brother in footballer Nathan Woolfe who is on the books at Connah’s Quay Nomads having previously played for Bolton Wanderers and Wrexham. And he reached the height of cool when he was crowned Manchester’s first break dance champion in 1984 at the age of 17.