Ulster and Munster’s Champions Cup clashes with Oyannax and Stade Francais respectively will be played in the second week of January.
The games, both in France, were two of many postponed in the wake of the Paris attacks.
After talks between EPCR, the Ligue Nationale de Rugby, Premiership Rugby and Pro12 Rugby, those fixtures will now go ahead on the weekend of January 8/9/10.
The Champions Cup games between Racing 92 and Glasgow Warriors, Bordeaux-Bègles and ASM Clermont Auvergne, RC Toulon and Bath Rugby – as well as the Challenge Cup meeting of Pau and Castres Olympique – have all been rescheduled for the same weekend.
The Round 13 fixtures in the Top 14 will now be played later in the season, as will the Round 12 fixtures in the Pro12 between Ulster Rugby and Newport Gwent Dragons, Zebre and Glasgow Warriors, and Cardiff Blues and Munster.
The Premiership Round 9 match between Bath and Sale Sharks, which was due to be played on Friday, January 8, will also take place later in the season on a date to be announced.
Ulster's belated opening to their European campaign ended in a 27-9 defeat to Saracens at Ravenhill, while Munster opened with a 32-7 bonus-point win against Treviso.
Postponed matches to be rescheduled on January 8/9/10 2016
Champions Cup – Round 1: Oyonnax v Ulster Rugby, Racing 92 v Glasgow Warriors, Bordeaux-Bègles v ASM Clermont Auvergne, RC Toulon v Bath Rugby. Round 2: Stade Francais Paris v Munster Rugby
Challenge Cup – Round 1: Pau v Castres Olympique
