Saturday's United Rugby Championship games involving Ulster and Glasgow in South Africa have been postponed because of gastroenteritis infections in the travelling squads.
A URC statement said "it is not possible for Ulster or Glasgow Warriors to field full playing squads".
Ulster were scheduled to face the Sharks in Durban and Glasgow taking on the Lions in Johannesburg.
The URC said it would examine "potential dates" for rearrangements.
Ulster edged out the Lions last Saturday in the first match of their two-match URC trip to South Africa.