Six Tottenham first-team players and two members of backroom staff are believed to have tested positive for Covid, and Spurs are waiting for the results of PCR tests to confirm the extent of the problem.
Under current rules, players who test positive must self-isolate for 10 days.
Rennes are already through to the last 16 of the competition as group winners while Tottenham currently leads Vitesse on goal difference in the battle for second place.
Calling off the Europa Conference game appears unlikely as, according to UEFA rules, a team needs to have fewer than 13 available players or no registered goalkeeper available for that to be the case.
After facing Rennes, Antonio Conte’s side returns to Premier League action with a trip to Brighton on Sunday, before they travel to Leicester City next Thursday and host Liverpool on December 19. The 10-day period of self-isolation for anyone who tests positive means Spurs’ players hit by the outbreak are set to miss their next three games.