Ukip MEP Steven Woolfe was punched in the face, new medical evidence suggests.
Sources told ITV News that "bruises consistent with a punch" were found by a team of independent experts.
Mr Woolfe was involved in an altercation with fellow Ukip MEP Mike Hookem in Strasbourg on Thursday.
Mr Hookem "absolutely" denies being responsible for Mr Woolfe's injuries and claims he acted in self-defence during a "scuffle".
Nigel Farage has launched an inquiry into the "nasty altercation" between Ukip MEPs Steven Woolfe and Mike Hookem.
Mr Farage, who admitted he is back in temporary charge of the party, said he hopes to have established what exactly happened by next week.
"I've launched an investigation: two senior party officers will take witness statements from everybody inside and outside that room and we will know by the middle of next week exactly what happened", he said.
The 52-year-old added: "He [Steven] has suffered two nasty seizures.
"I don't know how long he's going to be in hospital but you know he's been through a very, very rough experience".
Sources told ITV News that "bruises consistent with a punch" were found by a team of independent experts.
Mike Hookem insisted he acted in self-defence during a "scuffle" with Ukip leadership favourite Steven Woolfe.
As Ukip and the European Parliament investigate the 'altercation' between Steven Woolfe and Mike Hookem, what could the repercussions be?