Friday night's Heineken Champions Cup meeting of Montpellier and Leinster is in doubt, with COVID-19 outbreaks at both clubs.
Leinster postponed Monday's training sessions after a number of positive cases were made know after Saturday's win at home to Bath.
Meanwhile, RMC Sport reported that two Montpellier players tested positive for coronavirus on Monday morning, following Saturday's 42-6 defeat away to Exeter Chiefs.
Leinster opened their Group A campaign with a 45-20 win over Bath at the Aviva Stadium on Saturday afternoon.
"Given the positive Covid-19 cases in Leinster Rugby ahead of Saturday’s Heineken Champions Cup game against Bath Rugby," a statement read, "Leinster Rugby will undergo another full round of antigen and PCR testing at its UCD base today.
"As a further precaution, until all results are confirmed, today’s training in UCD has been postponed until tomorrow.
"The IRFU and EPCR have been consulted in advance of this decision which has been taken in the best interests of Leinster Rugby players and staff."
Two members of Montpellier staff tested positive on Friday, followed by two players on Monday.
Training was suspended as a result, with players and staff tested before being sent home to isolate.
Last weekend saw Bristol Bears awarded a 28-0 bonus point win by tournament organisers EPCR, as their opponents Scarlets were unable to fulfil their Pool B fixture.
However, EPCR guidance is unclear as to the outcome if two teams are unable to field teams.