European Champions Cup: Who can still qualify?

Back-to-back champions Saracens face elimination at the pool stage

The top table of European rugby is about to get even more exclusive.

Come Sunday evening, the pool-stage music will stop and only eight seats will remain, filled by the Champions Cup quarter-finalists.

Before the final round of matches, the hopes of some of the continent's heavyweights hang by a thread, with only Leinster having secured their place.

Saracens began the season hunting a third successive title, but their place in the last eight depends on other results going their way.

Irish powerhouse Munster are top of Pool Four but not safe, while Ospreys and Scarlets could ensure Welsh representation in the knockout stages for the first time in six years.

Here are the ramifications and calculations for a tightrope-tense climax to the pool stages.

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State of play

The five pool winners qualify automatically for the quarter-finals, with the four sides with the most points getting home advantage.

They will be joined by the three best second-placed teams.

Who else has a chance?

What if teams from different pools finish level on points?

If two teams are tied on points, the club with the best aggregate points difference from games in the pool stage will progress.

Failing that, the team with the most tries from the pool stage goes through. If that is equal, progression is decided by the club with the fewest number of players suspended. If they still cannot be separated, they will draw lots.

What if teams in the same pool are level?

If two teams in the same pool tie on points, their ranking is determined by the results of the two matches played between the sides in the pool stage.

The team with the most match points from the two games goes through. If equal, it goes down to the club with the best aggregate points difference from the two meetings.

Finally, it will come down to the side that scored the most tries in the two matches.

Pool One

Remaining fixtures: Wasps v Ulster, La Rochelle v Harlequins (21 January)

Ulster are in pole position to qualify after their win over La Rochelle last weekend.

They travel to the Ricoh Arena to face Wasps, knowing a bonus-point victory will confirm them as group winners regardless of La Rochelle's result against bottom side Harlequins.

La Rochelle will win the group if they win and Ulster lose, or if they can secure a bonus-point victory over Quins and Ulster do not score four tries. That would leave both teams on 21 points, but the Top 14 side have a better match points haul from their two games against Ulster.

Wasps need a bonus-point win over Ulster to stand any chance of staying in contention, but that would depend on Ulster not securing a losing bonus point and La Rochelle's result.

Harlequins are already eliminated.

Pool Two

Remaining fixtures: Saracens v Northampton, Clermont v Ospreys (20 January)

The top spot will be claimed by the winner of Clermont v Ospreys.

If Ospreys win, Clermont are guaranteed second place because they won both their games against Saracens.

Defending champions Saracens, who last failed to get out of the pool stages in 2011, need a win against Northampton - coupled with a Clermont victory or draw against Ospreys - to claim second spot.

Northampton are already eliminated.

Pool Three

Remaining fixtures: Montpellier v Leinster, Glasgow v Exeter (20 January)

Leinster are through as group winners, leaving Exeter and Montpellier to battle it out for second place.

Exeter's equation is simple: they will be a runners-up with a win in Glasgow, putting them on 18 points.

Montpellier would draw level on points with Exeter with a bonus-point win over Leinster, but they lost both group games against the English club so would not qualify in that scenario.

The French side's only hope is to beat Leinster and for Glasgow to beat or draw with Exeter.

Glasgow are already eliminated.

Pool Four

Remaining fixtures: Leicester v Racing, Munster v Castres (21 January)

Bar Leicester, Pool Four is the tightest group.

Munster, Castres and Racing 92 can all go through and all be eliminated.

If Munster beat Castres and score four tries they will go through as pool winners and Castres will be eliminated.

A win for Castres would see them qualify ahead of the Irish side because they drew their home game against Munster so would have a better head-to-head record in the group.

If Munster lose, they would be eliminated if Racing 92 beat Leicester.

Leicester are already eliminated.

Pool Five

Remaining fixtures: Benetton v Bath, Scarlets v Toulon (20 January)

If the Scarlets beat three-time winners Toulon they will win the pool. French side Toulon need a win or draw in Wales to guarantee progress, although a losing bonus point would almost certainly be enough too.

If Toulon lose without gaining a losing bonus point they would be eliminated by a Bath bonus-point victory against Benetton.

Bath would qualify as runners-up because they would be level on 18 points with Toulon, going through because they outscored the French side 46-45 over their two games.

If Scarlets lose without picking up a bonus point they too would be eliminated by a Bath bonus-point victory. However, if the English side do not secure a bonus point, Scarlets would go through because they outscored Bath 48-35 in their two matches.

Benetton are already eliminated.

Irish on top, English struggles and the resurgent Welsh - analysis

BBC rugby reporter Christopher Jones

Unlike two seasons ago, when five English sides reached the quarter-finals of the Champions Cup, there is a genuine prospect that no Premiership outfit will qualify for the knockout stages, with the likes of Exeter, Bath and Saracens all looking for a runners-up spot and an away quarter-final at best.

While the English toil, the Irish provinces look to be back as strong as ever - Leinster especially - while it is also heartening to see an uplift in performance from the Welsh sides.

The regions have barely made a scratch on Europe over the past decade, but both Scarlets and Ospreys go into the final round of pool matches with everything to play for.

While the Ospreys' chances of progression are a little slim, the Scarlets can top their pool by beating Toulon - and a home quarter-final would ensure Wayne Pivac's side are genuine title contenders.