Welsh scrum-half Mike Phillips was admitted to hospital after being attacked in Cardiff city centre, his club said today.
The 26-year-old was believed to be on a night out in the Mill Lane area of Cardiff during the early hours of this morning when he was assaulted.
One onlooker said a crowd of people gathered around the injured 6ft 3ins 16-stone player after the incident.
A spokesman for his club, the Ospreys, said Phillips was taken to hospital as a precautionary measure, but was discharged following a check-up.
Phillips, who has 33 caps for his country, had minor keyhole surgery only last week on a knee injury that has sidelined the player since March. He is expected to return to action in December - ruling him out of Wales' Autumn tests.
South Wales Police are now investigating the incident and trying to trace the player's assailant.
A spokesman for the Ospreys said: "The Ospreys can confirm that Mike Phillips was attacked in Cardiff city centre in the early hours of Sunday morning.
"He was subsequently taken to hospital as a precautionary measure and, following a check-up, was discharged from medical care.
"He did not sustain any permanent injuries."
The spokesman added: "The matter has now been reported to the police and we await the outcome of their investigations."
A spokeswoman for South Wales Police said: "A 26-year-old man was assaulted in the Mill Lane area of Cardiff city centre at around 4.15am on Sunday October 19.
"He was taken to hospital with facial injuries. Inquiries are ongoing in relation to tracing the suspect."