The weekend's Premiership matches at Worcester and London Irish have been called off because of Covid-19.
It comes after 33 new cases were found at 10 clubs in the latest round of testing - the most this season.
Harlequins were due to visit Worcester on Friday but one of their squad was found to have the virus and a further six players have been ruled out after a "forensic contact tracing process".
Irish were due to host Northampton on Sunday, but returned positive tests.
The Exiles said "a number of positive tests" had been discovered in the latest round of testing, and players were unavailable because of contact tracing protocols.
Director of rugby Declan Kidney said: "We're disappointed because we feel we still had a strong group of players to select from, but due to Public Health England guidelines, we've been told we're not allowed to play the game."
Earlier, Harlequins said they would be unable to field a front row at Worcester following their test results.
Of the 33 people who have tested positive in the league, 24 are players and nine are staff.
Quins have also cancelled training for a week to stop "further transmission".
The London club said "standing players down" is to "minimise the use and possible contamination of the training facility" and that they were doing so to "protect the health and wellbeing of players and staff".
Worcester have said they "support" the cancellation of the match and that "the safety of players, officials and staff in these worrying times is the sole consideration when making these decisions".
The cancellations mean four Premiership games have been called off in the past week because of the coronavirus pandemic, with Boxing Day fixtures between Newcastle and Leicester and Bath and London Irish also not going ahead.
A league panel awarded both Newcastle and Bath four points, while Tigers and Irish were given two.
The panel will again convene to decide how points are allocated to the four clubs affected in this latest round of games.
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