Jack Widdowson, 19, from Bath, remains in intensive care with serious neck injuries after being assaulted while out with his brothers in Cardiff.
His mobile phone was stolen and he was left unconscious in the street.
Officers confirmed they had arrested a 23-year-old man in Broadway, Roath, Cardiff, on suspicion of assault and robbery.
News of the arrest came after Mr Widdowson’s father issued a plea for people to come forward with information about Saturday’s attack, which happened when the teenager became separated from his brothers on a night out.
Mr Widdowson, an apprentice dancer at Bern: Ballett based at the Stadttheater Bern in Switzerland, had been visiting his brother – a former semi-professional rugby player – at Cardiff University.
South Wales Police said Mr Widdowson was attacked on a towpath near a disused canal and had his property, including his iPhone, stolen.
He was found unconscious by a member of the public shortly after 2am on Saturday before being taken to hospital where his family have been at his bedside.
His Cardiff-born father Dr Julian Widdowson said: “We are all appalled by this unprovoked, mindless violent attack.”