Exeter's defence of their Champions Cup crown has suffered a setback following the cancellation of Sunday's match against Toulouse because of an outbreak of coronavirus.
The Chiefs have reported a number of positive tests for Covid-19 and are unable to fulfil the round two fixture at the Stade Ernest Wallon.
The knock-on effect is that Glasgow - Exeter's opponents last weekend - are unable to field a side against Lyon due to the need for 20 of their players to self-isolate, meaning their game is also cancelled.
Tournament organisers EPCR will convene a match resolution panel to decide the result of the games once all four clubs have submitted their testing results.
If a 28-0 defeat is awarded against Exeter, it will place them on the back foot in their quest to advance to the knockout phase as the truncated format to this year's competition consists of only four group games.
The Chiefs thumped Glasgow 42-0 to launch their campaign with a statement win and have only two remaining fixtures - against Toulouse and the Warriors in January - to secure their place in the quarter-finals.
Their clash with Toulouse - in a replay of last season's semi-final - was the most eagerly-awaited fixture of round two and their first true test of 2020-21.
"EPCR has been informed that a number of Exeter players and staff have tested positive for COVID-19, and that in accordance with public health guidelines, the club will not be able to send a matchday squad to fulfil its fixture against Toulouse. The Pool B match is therefore cancelled," a statement read.
"As Exeter played against Glasgow in round one of the tournament, Glasgow Warriors have advised EPCR that many of its senior players are now self-isolating in accordance with guidelines from Public Health Scotland and consequently the club is not in a position to field a matchday squad of the appropriate standard for its round two fixture against Lyon.
"The Pool B match between Glasgow Warriors and Lyon is therefore also cancelled.
"As per its COVID-19 protocol, EPCR will convene Match Result Resolution Committees to determine the results of the cancelled matches and the decisions of the committees will be communicated as soon as practicable."