Steven Woolfe has been discharged from hospital after an altercation with a fellow Ukip MEP.
The North West England representative has claimed his colleague Mike Hookem "came at him" in a scuffle outside a meeting in Strasbourg.
Mr Woolfe was taken to hospital with a suspected head injury after suffering from seizures and collapsing later that day.
Mr Hookem has denied punching Mr Woolfe and posted a photograph of his hands on Twitter.
The move came after Mr Woolfe issued a statement saying medical examinations suggested the bruising on his face was caused by more than just a fall or seizure.
An internal Ukip probe is to investigate the incident, with some senior figures saying it should bar leadership front-runner Mr Woolfe from continuing in the race to head the party.