Munster Rugby have confirmed a positive Covid-19 case in their squad, meaning they will not be departing South Africa today.
The province's game against the Bulls, due to take place yesterday, had been postponed earlier in the week after the discovery of the new variant of the illness called Omicron.
The squad had been undergoing PCR testing in their hotel in Cape Town when the case emerged.
It had been confirmed already that the travelling party would have to quarantine for 10 days upon their return to Ireland, but it's now unclear when they will make that journey.
A Munster statement read: "After arriving at their hotel in Cape Town late last night the squad underwent a round of PCR testing ahead of today's possible departure.
"The returning results have identified one positive case.
"In taking all precautions and prioritising the health and well-being of everyone, Munster Rugby will not travel today and will return to their hotel for an isolation period as a matter of priority.
"The province will await further guidance from the health authorities."
Cardiff also said they have been unable to depart following two positive cases, one of which is suspected to be the new variant Omicron.
The Welsh club said in a statement: "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."
Zebre chairman Michele Dalai had earlier tweeted that all four visiting sides would be flying from Cape Town at 12pm and landing in Dublin at 10pm.
Round seven fixtures, scheduled to take place in South Africa next weekend, have also been postponed.