The United Rugby Championship meeting between Ulster and Leinster has been postponed.
Due to take on Saturday at Kingspan Stadium, the game will now be rescheduled.
Orgainsers say the decision has been taken after the emergence of positive cases in the Ulster squad.
Leinster too had Covid issues in recent weeks, but were understood to be in a position to play.
Two other matches have been postponed too; Dragons' meeting with Cardiff and Edinburgh versus Glasgow will also be rescheduled.
Connacht's meeting with Munster on New Year's Day is set to go ahead at the Sportsground.
"The URC games were due to take place on Saturday and Sunday (January 1 and 2), however, a number of positive Covid-19 cases in Cardiff, Dragons, Glasgow Warriors and Ulster 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.
"The United Rugby Championship will now consider available dates to reschedule these games."
More to follow....