The latest edition of Europe's annual showpiece rugby union tournament is set to begin on the opening weekend of February, with no spectators because of Covid-19 restrictions.
But with the British and Irish Lions tour of South Africa in doubt because of the global pandemic, there have been suggestions that the Six Nations could be delayed by four months to take advantage of a gap in the schedule and allow matches to be played in front of fans.
As things stand, the 2021 Six Nations will begin on 7 February (AEDT), when Italy faces France in Rome and champion England welcomes Scotland to Twickenham for the Calcutta Cup.
Wales and Ireland are scheduled to complete the first round at Cardiff's Principality Stadium on 8 February.
"The Six Nations is planning for the tournament to go ahead as scheduled, but we are monitoring the situation with the unions and their respective governments and health authorities," a spokesperson said Monday.
There was a similar message from England's governing Rugby Football Union.
"We are committed to the fixtures, monitoring the situation with all parties and planning continues aligned with current guidelines," said an RFU spokesperson.
All the competing unions face losing significant revenue if matches are played behind closed doors, as happened towards the end of last year's competition.
The 2020 Six Nations finished at the end of October after a seven-month pause following the initial spread of Covid-19 across Europe.
Meanwhile, there are concerns that Covid-19 could lead to the postponement of the Lions' tour of South Africa.
An eight-match itinerary that culminates in a three-Test series against the world champion Springboks is set for July and August.
However, with Britain, Ireland and South Africa still in lockdown to try and bring down infection rate and the possibility of fans being allowed to travel and attend matches receding, the Lions said Saturday that a decision on whether the tour goes ahead a planned could be taken as soon as February.
The RFU said on Tuesday (AEDT): "We are continuing discussions with all parties and have no update beyond the recent statement from the Lions."
It has long been thought by many within British, Irish and South African rugby that a Lions tour without travelling supporters would not be commercially viable.
But holding over the Lions trip until 2022, just over a year out from the 2023 World Cup in France, may lead to clashes with already planned national tours.
England, which could provide the Lions with a large contingent of players, is set to tour Australia while Ireland is in New Zealand and Wales are due in South Africa.
A further difficulty for the Lions is that the new British and South African strains of Covid-19 are believed to be more transmissible than previous variants.