Ulster's New Year’s Day derby against Leinster has been postponed after Ulster reported a number of positive Covid-19 cases in their squad.
Coronavirus issues at both Dragons and Cardiff mean their planned round nine fixture in the United Rugby Championship on the same day will also be rearranged, along with Glasgow's trip to Edinburgh on 2 January.
"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," a URC statement read.
"The United Rugby Championship will now consider available dates to reschedule these games."
Ulster and Leinster’s St Stephen’s Day fixtures against Connacht and Munster respectively were also called off due to Covid.
Leinster, who returned to training on Tuesday following an outbreak in their squad, have not played since their Heineken Champions Cup mauling of Bath on 11 December.
Next month's home game against the Emirates Lions was also rescheduled, leaving Leo Cullen's side without a game for five weeks.
Ulster are due to travel to Thomond Park to face Munster on 8 January.
