London Irish's Premiership match with Bath on Saturday has been cancelled due to several of their players testing positive for coronavirus, Premiership Rugby announced on Wednesday.
Their game is the second to be cancelled following that of Newcastle's home match with Leicester after the latter revealed a large number of their players have to self isolate.
London Irish returned a small number of positive tests in this week's round of testing, but had further players who presented with symptoms on Tuesday.
"We were really looking forward to going to The Rec on Boxing Day (Saturday), so we're incredibly disappointed that we're unable to fulfil the fixture," said London Irish director of rugby Declan Kidney.
"I'm really disappointed for the players, as they've acted professionally, following all the relevant guidelines, but this is the situation we find ourselves in at the moment, as the country continues to try and navigate its way through the pandemic."
Champions Exeter, though, will be able to play Gloucester after undertaking additional rounds of coronavirus testing that have enabled them to get on top of the outbreak at the club.
The European champions had to forfeit their Champions Cup pool match against Toulouse last weekend when they returned a double-digit number of positives.
"We will have a pretty strong squad to pick from based on players who have completed their isolation and guys who have now tested negative three times in a row," Exeter's director of rugby Rob Baxter said on Wednesday.
Unlike in English football where matches can be postponed there is no such leeway in the Premiership.
"Under the Premiership Rugby regulations, the match between London Irish and Bath Rugby will be cancelled," read a Premiership Rugby statement.
"A Premiership Rugby panel will now be convened to determine the allocation of points and a further announcement will be made in due course."