Montpellier have been awarded a 28-0 win in Friday's scheduled Champions Cup game against Leinster in France because of the Irish province's Covid cases.
Leinster expressed "disappointment" after they had been given permission to travel by the Irish authorities.
However, the competition's match risk assessors made the adjudication following further Leinster Covid cases.
Earlier on Thursday, Leinster had announced a team which showed eight changes from the win over Bath.
Ireland quartet Jordan Larmour, Garry Ringrose, Hugo Keenan and Tadhg Furlong were among those to drop out of the squad after starting last week.
"The Match Risk Assessment Committee, made up of medical doctors from EPCR's [European Professional Club Rugby] Medical Advisory Group as well as an independent medical specialist with experience in virology, advised EPCR of its concerns following new positive Covid-19 test results from the Leinster Rugby playing squad, and regrettably the decision was made to cancel the match," said a statement from the competition's organisers.
Leinster's unspecified number of Covid positives
With Leinster reporting an unspecified number of Covid positives, academy back James Osborne had been due to start at centre with four other players in line for Champions Cup debuts after being named on the bench.
Fit-again James Ryan was set to captain the side with his fellow Ireland international forwards Dan Leavy and Jack Conan also named in the starting line-up.
Leavy and Conan were scheduled to partner Max Deegan in the back row as last week's captain Rhys Ruddock, Josh van der Flier and Caelan Doris were all missing after starting last weekend.
In addition to starting centre Osborne, Vakh Abdaladze, Jack Dunne, Cormac Foley and Scott Penny were also in line for European debuts after being named in the replacements.
Montpellier also hit by Covid outbreak
With Montpellier similarly hit by an outbreak of Covid within their ranks, there had been doubt throughout the week over the match taking place.
After being delayed from Thursday because of the Covid concerns, Leinster's charter flight from Dublin was then scheduled for Friday morning before word came through of the competition organisers' announcement.
The four-time winners had indicated that "an additional number of senior players" had tested positive for Covid-19 after three players and a member of staff had tested positive for coronavirus before the win over Bath.
For their part, Montpellier reported a fifth positive Covid-19 case in their squad on Tuesday.
They added that their squad had been training in separate groups this week before being tested again on Wednesday.
Two Montpellier staff members tested positive last Friday before the French side's comprehensive 42-6 defeat by Exeter, while a further two players were also found to have the virus following the side's return from England.
Tuesday's Montpellier statement did not detail whether their latest Covid positive was a player or staff member.
Montpellier: Darmon; Vici, Reilhac, Lucas, N'gandebe, Foursans, Aprasidze; Forletta, Maurouard, Haouas; Capelli, Willemse; van Rensburg, Gallatier, Tauleigne.
Replacements: Paenga- Amosa, Rodgers, Hamadache, Mercer, Eymeri, Bevia, Martin, Duguid.
Leinster: J O'Brien; A Byrne, Osborne, Frawley, Lowe; R Byrne, Gibson-Park; Healy, Kelleher, Porter; Baird, Ryan (capt); Deegan, Leavy, Conan.
Replacements: Sheehan, E Byrne, Abdaladze, Toner, Dunne, Foley, T O'Brien, Penny.