European Professional Club Rugby has relaxed player registration rules in response to the plight of four sides who found themselves stranded in South Africa but has stressed that there are no spare weekends to accommodate postponements.
Cardiff, Munster, the Scarlets and Zebre Parma have all faced difficulties leaving South Africa after their United Rugby Championship fixtures were postponed following the imposition of fresh travel restrictions due to the discovery of a new coronavirus variant.
The majority of players and staff from Munster and Zebre have since returned to Ireland and Italy respectively to complete their periods of isolation, but the Scarlets remain holed up in a quarantine hotel just outside Belfast and Cardiff are still waiting for a flight out of Cape Town.
The Scarlets urged EPCR to reconsider its position on the rescheduling of Heineken Champions Cup matches, with 32 of their players currently quarantining.
The Welsh region are due to play their tournament opener at Bristol on December 11, just a day after finishing their 10-day isolation period.
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A Scarlets statement said: "With the Welsh Government ruling that the squad that travelled to South Africa has to see out the full 10-day isolation period at a quarantine hotel outside of Belfast, Scarlets are urging European tournament organisers EPCR to reconsider their position on the rescheduling of matches."
However, EPCR issued a statement of its own later on Thursday, announcing an option for all teams to bolster their squads with an unlimited number of previously unregistered players while all but dismissing the possibility of rescheduling fixtures.
"Following consultation with the leagues and unions, it has been decided to extend the first registration date from last month to allow all participating clubs to supplement their squads with an unlimited number of previously unregistered players," read the statement.
"All new players will have to be registered on or before Wednesday, 8 December at midday (UK and Irish time).
"With no alternative weekends available in the 2021/22 season calendar, EPCR is in regular dialogue with the leagues and clubs to ensure that all possible measures are considered so that the matches take place as scheduled.
"While looking forward to another series of compelling pool stage fixtures, EPCR is mindful of how recent events have impacted on Cardiff Rugby, Munster Rugby, Scarlets and Zebre Parma in particular, and the tournament organiser would like to extend its best wishes to the players and staff who currently remain in South Africa, as well as to the players and staff who have been repatriated and are currently isolating."
Teams who are unable to fulfil European Cup fixtures face forfeiting the game under strict tournament rules.
Such a stance, though, drew criticism last season after a handful of coronavirus-related cancellations saw clubs responsible handed 28-0 defeats.
Scarlets executive chairman Simon Muderack said: "If we were to play Bristol without the people who are in Ulster right now, there are four or five positions where we physically do not have a body to fill that position."
Ospreys head coach Toby Booth said their neighbours the Scarlets had contacted them asking if they had any players available.
"They've asked for seven or eight," Booth said at a press conference before the Ospreys' URC home game with Ulster.
"We're willing to help out because it's important we see the bigger picture here. It will suit us giving people opportunities to play in a prestigious game.
"The boundaries are certainly softer when you have to contingency plan to that extreme, so it's about getting everyone in the tent together, helping each other out and looking after each other.
"Obviously we need to get player approval and EPCR need to agree around people not being cup-tied by playing, but hopefully common sense prevails and we can keep people playing."