Toulon's France scrumhalf Baptiste Serin said on Friday he questioned the return of the Top 14 next month due to various outfits noting positive coronavirus tests.
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On Monday Stade Francais, who begin the new season by hosting Bordeaux-Begles on 4 September, stopped training due to a reported 25 examples of Covid-19 within their squad and coaching staff.
Fellow top-flight side Lyon have also had instances as have Oyonnax, Provence and Soyaux-Angouleme in the second tier.
"With the cases recorded at certain clubs, you tell yourself we can't restart in three weeks," Serin said after his side's 38-all pre-season draw with Grenoble.
"Untill when will be able to play? Everybody's asking questions. We just have short-term visibility," he added.
Last term's Top 14 was stopped in April without a champion declared due to the pandemic.
European quarter-finals have been re-scheduled for mid-September with the Six Nations to be finished in late-October and a new eight-country tournament replacing the cancelled traditional November Tests.