Ulster's Heineken Cup quarter-final against Saracens will be played on Saturday, 6 April (18:30 BST), although the venue has yet to be finalised.
Saracens are exploring the possibility of staging the game on the club's new artificial pitch at Allianz Park.
Munster's quarter-final against Harlequins will take place at Twickenham Stoop on Sunday, 7 April.
Recent Heineken Cup winners
- London Wasps
- London Wasps
Clermont Auvergne face Montpellier on 6 April with Toulon taking on Leicester the following day.
As in the case with Ulster's clash with Saracens, the announcement of the venue for Toulon's clash with Leicester has been delayed.
Allianz Park is Saracens's preferred choice for the quarter-final, with Wembley or Twickenham potential alternatives.
But, if held at Allianz Park it would become the first European game to be played on an artificial surface.
Sunday's test event against Cardiff in the LV= Cup will be the first game played on the artificial pitch in front of a crowd of 3,500, three weeks before the official opening against Exeter in the Premiership on 16 February.
Saracens chief executive Edward Griffiths hopes Barnet Council will grant the club permission to temporarily increase the 10,000 capacity to 15,000 to comply with tournament organisers European Rugby Cup's rules for hosting quarter-finals.
Saturday, 6 April
ASM Clermont Auvergne v Montpellier, Stade Marcel Michelin, 15:40 BST
Saracens v Ulster, venue TBC, 18:30 BST
Sunday, 7 April
Harlequins v Munster, Twickenham Stoop, 14:00 BST
Toulon v Leicester Tigers, venue TBC, 17:30 BST