The New Year's Day clash between the Dragons and Cardiff has been postponed after a number of positive Covid cases were reported in both camps.
The Rodney Parade clash on January 1 will not go ahead - and neither will two other United Rugby Championship fixtures scheduled for this weekend.
Ulster's clash with Leinster and the Scottish derby between Edinburgh and Glasgow Warriors have also been postponed.
In a statement, the league explained that "a number of positive cases in Cardiff, Dragons, Ulster and Glasgow Warriors squads have been reported".
"The URC Medical Advisory Group has liaised with the medical teams at Cardiff, Dragons, Glasgow Warriors, Ulster and their respective health authorities and deemed that these fixtures cannot go ahead as scheduled," it read.
"The United Rugby Championship will now consider available dates to reschedule these games."
With both Welsh Boxing Day derbies called off due to Covid, this would have been the first game in Wales behind closed doors since restrictions on crowds were reintroduced.
However, that won't be the case now in another bitter blow for Welsh rugby fans.
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