Jeremy Corbyn's youngest son says he was headbutted as he left a nightclub.
Engineering student Thomas, better known as 'Tommy', suffered a cut to his eye after being assaulted outside the dance venue in the early hours of Saturday morning.
The 22-year-old, who was out with friends, had been helping put on a 'Party for Palestine' hip-hop event on Friday night before heading to York's Mansion club, where the man says he was assaulted.
He has since lodged a formal complaint to police, who are now investigating.
The nightclub Tommy says he was attacked outside
A statement from North Yorkshire Police said: "Police in York are investigating an allegation of assault on a 22-year-old man.
"The incident occurred at the Mansion Nightclub, Micklegate, between 4am and 4.30am on Saturday (27 February 2016).
"The victim, who suffered a cut to his eye, reported the matter to North Yorkshire Police at 1.26pm on Saturday.
"Enquiries are on-going to investigate the full circumstances surrounding the incident. Nobody has been arrested.
"Witnesses or anyone with information that could assist officers are asked to contact North Yorkshire Police on 101, select option 1, and speak to the Force Control Room."
Tommy is a left-wing activist who studies at the University of York, and has been seen at several of his father's speeches to support the Labour party leader.