Most of Munster's playing and backroom staff have arrived back from South Africa after being stranded in Cape Town due to the discovery of the new Omicron coronavirus variant.
The Irish province were stuck in the city following the cancellation of their scheduled cross-hemisphere matches in the United Rugby Championship.
Fresh travel restrictions were imposed on South Africa, and Munster and Cardiff had hoped to join the Scarlets and Zebre Parma in leaving on Sunday aboard a charter flight before positive cases caused a hold-up.
Despite announcing on Tuesday night that a further four members of the touring party had tested positive - adding to the 10 already confirmed - Munster said on Wednesday that 34 players and staff had arrived back in Ireland after receiving negative results from a fourth round of PCR testing in six days.
Munster, who will now isolate at home, are due to face European Cup opponents Wasps on December 12, while Scarlets' travelling group from South Africa is currently isolating at a Belfast hotel. Their scheduled European opener is against Bristol on December 11.
Academy manager Ian Costello is overseeing Munster training ahead of their Champions Cup opener, with senior and academy players who did not travel to South Africa having started working together on Monday.
A Munster statement added: "EPCR (European Professional Club Rugby) are aware of the situation and in contact with the province."
Cardiff have revealed plans to travel to quarantine accommodation in England on Thursday.