Leinster's Heineken Champions Cup last-16 match against Toulon has been called off after an unnamed Toulon squad member tested positive for Covid-19.
The French side were already in Dublin in preparation for the Friday evening fixture.
With the quarter-finals scheduled for next weekend, it appears unlikely that the fixture will be rearranged.
The winner of Friday's match was set to meet Exeter Chiefs or Lyon on Friday 9 April.
The Toulon player tested positive before the side left France, and subsequently did not travel with the squad.
However, despite an additional round of testing on Thursday returning all negative results, European Professional Club Rugby's matchday medical risk assessment committee identified a number of players as "high risk contacts" and therefore unsafe to play.
"Having been notified of that position, RC Toulon informed EPCR that they could not select a match day squad to safely fulfil the fixture," said an EPCR statement.
During the group stages of the tournament, any side unable to fulfil a fixture due to a Covid-19 case were deemed to have lost the game. Should the same principle apply to the knock-out stages, Leinster will advance to the last eight.
This season's competition has looked radically different to its usual format, and has had to contend with the challenges posed by the ongoing pandemic.
January's remaining pool fixtures were scrapped following French government concerns regarding cross-border travel.
The semi-finals are scheduled for the weekend of 30 April with the final set to take place on Saturday 22 May, although it will no longer be held in Marseille.