Cardiff Rugby have been unable to leave South Africa after two positive Covid cases were identified, including a suspected case of the new variant Omicron.
The team traveled to compete in the United Rugby Championship, but their games were postponed when South Africa became the first country to detect the new variant.
Cardiff Rugby said the travelling party had hoped to leave Cape Town on Sunday afternoon after securing a charter plane, but PCR tests taken on Saturday night returned two positive results.
Scarlets, who were also in South Africa for the tournament, confirmed on Sunday that their travelling squad and staff have flown to Europe.
Two cases of Omicron were confirmed in England on Saturday. South Africa and some other African nations have been added to UK red lists for international travel.
The variant has since been confirmed in 13 people who arrived in the Netherlands from South Africa on Friday.
A spokesperson said: "As a consequence of one of these results suspected of being Omicron, the entire travelling party have returned to their hotel to isolate.
"Cardiff Rugby continue to work with the South African Rugby Union, the Welsh Rugby Union and public health authorities both at home and abroad to decide the next course of action.
"The club are also continuing to work with all relevant authorities to secure the travelling party's return to Wales when safe and appropriate.
"Everybody concerned in this highly challenging situation would like to thank their families, friends, colleagues and the wider rugby family for their many messages of concern and well wishes."
Commenting on the news, a Welsh Government spokesperson said: "We are sorry to hear some of those travelling with Cardiff Rugby have tested positive for coronavirus while in South Africa.
"We wish them a speedy recovery and look forward to seeing the team and staff back in Wales."