The ERC has confirmed the schedule for Rounds 5 and 6 of the Heineken Cup, with Leinster and Northampton given short breaks between games.
Former champions Leinster will take on Castres at Stade Pierre Antoine on Sunday, January 12 before hosting the Ospreys the following Friday.
Pool rivals Northampton meanwhile are in the same boat for their two remaining showdowns.
In other groups, the brand new Allianz Riviera in Nice will stage a Heineken Cup fixture for the first time when Toulon tackle Cardiff Blues in their critical Pool meeting on Saturday, January 11.
Toulouse and Saracens face off in a key contest at Stade Ernest Wallon on Sunday, January 12.