These European fortnights are like London buses.

The action returns this weekend, and in the Champions Cup in particular the Guinness PRO14 clubs are staking a serious claim at the top table.

So here are five questions to keep an eye on in round three this weekend

Do Leinster stick or twist?

Felipe Contepomi has alluded to it this week already.

Leinster’s youthful ‘second-stringers’ have laid waste to the league so far this season.

Felipe Contepomi provided an update on Seán Cronin today ahead of the #ChampionsCup clash with Northampton on Saturday. 👇#NORvLEI #JoinTheRoar pic.twitter.com/YGcXwA6TAO
— Leinster Rugby (@leinsterrugby) December 2, 2019

The defending champions are unbeaten and went to Glasgow Warriors, the runners-up from last season, and buried them on their own patch.

But how much longer can the likes of Will Connors be ignored when it comes to European rugby?

Leinster are two from two in Europe, but this weekend is the first of back to back clashes against Northampton Saints who are in top form and top of the table in England.

The boys in blue were not at their best last time out in Europe at Lyon, and maybe Leo Cullen will turn to his young guns this weekend to give life to their chase for a record fifth European title.

Have Munster made the step up?

Munster have lost at the semi-final stage in Europe in each of the last three seasons.

Twice their conquerors at that stage have been Saracens. So who better to come to Thomond Park this weekend than the men in black to give Johann Van Graan’s side an acid test.

Drawing at home last time out in Europe against Racing 92 means this Pool looks like it will go right down to the wire.

And while Munster are still without playmakers Joey Carbery and Tyler Bleyendaal, the vast majority of their starting XV are well rested and itching to get one over their nemesis.

Are Glasgow Warriors and Connacht serious contenders?

Both Connacht and Glasgow Warriors come into the Christmas double headers knowing it will decide their European fates.

Both won their first games at home and then lost on the road to open proceedings in their respective Pools.

Connacht therefore head to Kingsholm this weekend knowing that a loss their against the only team winless in Pool 5 so far could be curtains.

The Cherry & Whites have made it clear they are now prioritising the Premiership so if Andy Friend’s side are entertaining thoughts of being European knockout artists, that is a must-win game.

Dave Rennie’s Glasgow are struggling domestically, the head coach himself admitted as much last weekend in saying that top spot in Conference A was already gone.

After downing Sale at home, they got walloped in the second half at Sandy Park and now head, like Connacht, to the only winless side in Pool 2 La Rochelle. Victory is a must if Rennie’s side are to make the last eight as they did last year.

Can Ulster stay perfect?

Dan McFarland is becoming a pretty canny European operator.

If Jacob Stockdale doesn’t drop the ball at the Aviva last season, they would have made the semi-finals.

This time around they are a perfect two from two in Pool 3 and welcome Harlequins to the Kingspan this weekend looking to make it three from three.

📸📸📸 👉@Dicksondigital pic.twitter.com/BQR7cOWUF0
— Ulster Rugby (@UlsterRugby) November 30, 2019

Their home record under McFarland is sublime and Quins’ away form is patchy at best, this should be another home banker and then they take proper control of the group.

John Cooney cannot stop scoring tries, Stockdale and Iain Henderson are back and Robert Baloucoune on the wing proved he is a European finisher par excellence last season.

Ulster have won each of the last three meetings with Quins, including doing the double at Christmas two years ago. History is on their side and so will the support on Saturday night.

Are the Dragons still breathing fire?

The Dragons are the only Guinness PRO14 to have won two from two in the Challenge Cup.

But they take that unbeaten record to Sixways this weekend as Dean Ryan takes on his former club.

The Newport side need a boost after last weekend’s thumping on home turf by Zebre, but the Warriors are in fine form in the Premiership and currently sitting pretty in fourth.

If the Dragons’ campaign falters, the next best hope for the Guinness PRO14 probably lies with Edinburgh.

Richard Cockerill’s side made the quarter-finals in this competition last time they were in it, and also in the Champions Cup back in April, but back to back games against Wasps this Christmas will decide their fate this time around.