South African sides Cheetahs and Southern Kings will not play in the Pro14 for the rest of 2020, missing the start of the 2020-21 season.
Southern Kings have announced they will not be playing again this year.
Pro14 have confirmed Southern Kings and Cheetahs will not begin the 2020-21 season scheduled to start on the opening weekend of October.
The 12 teams from Wales, Ireland, Scotland and Italy will begin the new campaign.
After more than a five-month break because of coronavirus, the 2019-20 season regular season will conclude at the end of August before semi-finals and a final in September.
A Pro14 statement read: "Pro14 Rugby is aware of the Southern Kings voluntary decision to withdraw from any domestic competitions in South Africa for the rest of the 2020 calendar year.
"Due to on-going travel restrictions enforced by the South African government against the backdrop of the Covid-19 pandemic, it is not foreseen that any cross-border Guinness Pro14 games involving South Africa teams will take place until 2021.
"Pro14 Rugby remains in discussion with SA Rugby on when South African participation in the league can resume in the new year.
"Work is already underway to concentrate the opening 2020/21 fixtures among the 12 European-based clubs."
Tournament organisers are now working on different scenarios which includes seeing the South African sides join the season in 2021 or finishing the tournament with the 12 sides they start with.
One plan is to play 11 rounds from October up until Christmas with each team playing each other once. If South African teams still can't travel in 2021, they will just reverse those fixtures in the new year.
If the Cheetahs and Kings are able to play in 2021, league bosses hope they can still play fixtures against the South African sides next year.
An adventurous plan is to introduce the four Super Rugby sides Sharks, Bulls, Lions and Stormers into the Pro14 to become a Pro16.
This could happen be as early as the 2020-21 season with the South African sides playing each other in fixtures in late 2020 before facing the European sides in early 2021.
Southern Kings chairman Andre Rademan said "hard, financial realities" meant their season could not continue.
He added: "We now have time to consider what is the best way forward for rugby in the Eastern Province in this fluid and financially challenging environment."
Rademan is part of a board brought in by SA Rugby in June to oversee an organisation that has struggled financially.
In a statement confirming the end of their season, Kings said they had "voluntarily withdrawn the team from participation in any planned domestic rugby competitions in 2020" following an urgent meeting on Monday.
Rademan said: "Following several weeks of interrogation of the Kings' financial state of affairs we were left with a straightforward choice.
"We could opt to field the Kings in the domestic competitions mooted by SA Rugby for the sport's post-lockdown resumption if we so wished.
"If we did so, it would require additional loans to the Kings or extra investment from the shareholders to the tune of R6.5m (£295,000), which would add to the organisation's existing substantial debt.
"However, as there was no contractual requirement for the Kings to resume short-term participation in the Guinness Pro14 competition, because of air travel restrictions, and as the Kings had no other commercial commitments to honour, the most prudent decision was to withdraw.
"This may not be a popular decision, but in the current circumstances it is the right decision."
Kings' board say shareholders SA Rugby and Eastern Province Rugby Union (EPRU) backed their move.
"This is obviously very disappointing news for the players and management who, like all rugby professionals, were desperate to resume playing," said Rademan.
"But the board believed that further investment in 2020 with zero commercial return would be reckless in the extreme."