Leinster's European Champions Cup last 16 match with Toulon on Friday was cancelled just hours before kickoff after a player from the French side tested positive for coronavirus.
On the basis of matches already cancelled in this season's competition it is likely Leinster will be awarded the match.
The Toulon squad were already in Dublin for the eagerly anticipated game between four-time winners Leinster and the three-time champions that was due to kick off at 1630 GMT.
"This afternoon’s Champions Cup Round of 16 match between Leinster Rugby and RC Toulon at The RDS Arena in Dublin has been cancelled," European Professional Club Rugby (EPCR) said in a statement.
The winner of Friday's match has been drawn to meet 2020 champions Exeter Chiefs or Lyon on April 9.
Toulon president Bernard Lemaitre said the club were angry they were allowed to travel to Dublin even after the unnamed player had tested positive.
"It's infuriating. The player was tested positive on Wednesday and isolated immediately," Lemaitre told rugbyrama.fr.
"The EPCR was informed immediately... And despite a re-test of the (remaining) players last night that proved negative, these people have taken the decision less than five hours before the match."
During the group stages of the tournament, any side unable to play a fixture due to a Covid-19 case forfeited the game.
If the same principle is applied to the knockout stages, Leinster would advance to the last eight.
This season's competition has been heavily disrupted by the pandemic.
The remaining pool fixtures in January were scrapped following French government concerns regarding cross-border travel.
And the final, due to take place on May 22, was this week moved from the French city of Marseille for a second year running due to the pandemic.