The United Rugby Championship match between Ulster and Connacht on 26 December has been postponed because of a number of positive Covid-19 cases within the Ulster squad.
Potential new dates for the interprovincial derby, due to take place at Belfast's Kingspan Stadium, are being considered by the URC.
"The URC Medical Advisory Group has liaised with Ulster Rugby and the local health authorities and deemed that the fixture cannot go ahead as scheduled," Ulster said in a statement on Friday.
The match had been given the go-ahead to take place earlier this week when the NI Executive opted not to impose any new Covid-19 restrictions on Northern Ireland sport.
It was due to be Ulster's first home interprovincial derby of the season, and the first of three games against Irish provinces in as many weeks.
On New Year's Day, Ulster are due to host Leinster at the Kingspan Stadium, then on Saturday, 8 January Dan McFarland's men travel to Thomond Park to take on Munster.
Connacht won the last meeting between the sides at the Aviva in October but Ulster are nine points ahead of them in the URC table.
Meanwhile, Munster hooker Declan Moore has joined up with the Ulster squad as short-term injury cover.
New-Zealand born and Irish-qualified, 25-year-old Moore made his senior debut for Munster in this month's European Champions Cup match against Wasps.
Phone: (800) 737. 6040
Fax: (800) 825 5558
Website: 
Email: 
