Racing 92 on Thursday said that tests at the French rugby club had produced "several" positive cases of Covid-19 just over two weeks before they face English club Exeter Chiefs in the European Champions Cup final.
"Tests carried out on the group on Wednesday morning have revealed several positive cases," the club said, without saying if the cases concerned players or members of the coaching or medical staff.
Sources said that there were nine positive cases, also without identifying who had been infected.
Racing are set to play Exeter in Bristol on 17 October in European club rugby's showpiece final.
According to coronavirus protocols put in place by the LNR, the body that runs professional rugby union in France, Racing's away Top 14 game at La Rochelle set for Saturday has been postponed to a later date, yet to be decided.
The LNR has said that matches should be postponed should there be more than three players who test positive over seven consecutive days.
Racing have won their opening four matches of the season and saw off English club Saracens 19-15 in the semi-final of the European Champions Cup to earn the right to face Exeter.
The English side beat Toulouse 28-18 in the other semi-final.