Cardiff Blues have confirmed that centre Owen Williams has suffered a "significant injury to his cervical vertebrae and spinal cord."
The 22-year-old, who has played four times for Wales, was injured playing for Cardiff Blues at the World Cup 10s on Sunday.
The region said that he underwent an operation on Monday to stabilise a fracture and is currently recovering in hospital in Singapore.
His family and Blues staff are with him in hospital, and arrangements are now being made to arrange his safe transfer home "at an appropriate time."
The region and Williams' family have also thanked hundreds of people who have offered messages of support.
More top news
Exclusive figures given to ITV Cymru Wales show a steep rise in the number of people seeking advice for steroid use.
Cold, breezy and generally cloudy at first with further wintry outbreaks on the hills
All primary and secondary schools in Wales have been categorised in a new colour-coded system. Is your school green or red?