All four Welsh teams will go through to the knockout stages of Europe amid revised formats for the two cup competitions.
The Scarlets will appear in the last 16 of the Champions Cup, while Cardiff Blues, Ospreys and Dragons will figure in the last 16 of the Challenge Cup, with matches played on the weekend of April 2-4.
This follows the cancellation of the final two rounds of group fixtures in January due to Covid-19 issues.
Competition organisers EPCR have decided to push ahead and complete the European season, but with a rejigged structure.
The original plan was for only eight teams to progress to the knock-out stages of the Champions Cup, with home and away quarter-finals.
But now all the sides involved in that top tier event will have further matches to play, in recognition of some teams being adversely affected by Covid cancellations.
The top eight sides from each Champions Cup pool after the opening two rounds - including the Scarlets - will go through to the last 16 of that competition.
Then the other eight sides, one of whom are the Dragons, will drop down to the Challenge Cup to join the top eight from that competition, including the Blues and Ospreys.
The last 16 and quarter-final matches in both tournaments will be decided by draws which will take place on Tuesday, March 9.
For the purposes of the draw, clubs from the same league cannot be drawn against one another. However, clubs from either pool can be.
Teams which have won both of their Champions Cup pool matches on the pitch - where results were not impacted by Covid - will play at home in the round of 16. Therefore, Racing 92, Leinster, Wasps, Bordeaux-Bègles and Munster will each be guaranteed a home fixture.
The Scarlets wait to learn who they will face.
Similarly, teams which have won both Challenge Cup matches on the field will play at home in the last 16. The Ospreys are one of those.
The knockout stages will continue with quarter-finals, semi-finals and the scheduled Marseille finals.
Open draws will take place to determine the quarter-finals in both competitions, allowing for the possibility of matches between clubs from the same league.
European knock-out stages
Heineken Champions Cup: Racing 92, Leinster, Wasps, Bordeaux-Bègles, Munster, Lyon, Toulouse, La Rochelle, Scarlets, Clermont Auvergne, Bristol, Exeter, Edinburgh, Gloucester, Toulon, Sale Sharks
* Racing 92, Leinster, Wasps, Bordeaux-Bègles and Munster are guaranteed home matches in the last 16.
Challenge Cup: London Irish, Ospreys, Leicester, Cardiff Blues, Zebre, Agen, Benetton, Newcastle, Ulster, Connacht, Northampton, Bath, Montpellier, Dragons, Harlequins, Glasgow.
*London Irish, Ospreys and Leicester Tigers are guaranteed home matches in the last 16
Key Dates
Knockout Stage Draws: Tuesday, 9 March
Rounds of 16: 2/3/4 April
Quarter-finals: 9/10/11 April
Semi-finals: 30 April – 1/2 May
Challenge Cup final: Marseille - Friday, 21 May
Heineken Champions Cup final: Marseille - Saturday, 22 May
