A potentially defining weekend for Irish sides in Europe

On the first of two defining weekends for the Irish provinces in Europe, Leinster and Munster could both qualify for the knockout stages of the European Champions Cup tomorrow with a game to spare, as could Connacht in the Challenge Cup this afternoon, while Ulster could take a giant stride towards the same objective.

Alternatively, each or all of them could be taken to a nervy final round next weekend.

Leinster host Glasgow at 1pm in the RDS tomorrow knowing that a fifth win in five matches will assuredly see them advance, at the very least as one of the pool runners-up. Provided their result exceeds Montpellier’s result away to Exeter this afternoon, it would put them in the quarter-finals as pool winners.

In other words, anything less than a win for Montpellier would leave Leinster knowing that a victory of any kind would suffice. Were Montpellier to win without a bonus point, a bonus point win for Leinster would seal first place in Pool Three. Were Montpellier to win with a bonus point, Leinster would need to match that to maintain their five-point lead over the French team before meeting them away next Saturday.

Connacht braced for formidable Worcester test

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Ulster need a big improvement to keep European hopes alive

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Champions Cup pool previews

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Leo Cullen: ‘That was as nervous as I have ever been before a game’

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On confirming that young man of the moment, Jordan Larmour, will make his full European debut ahead of Rob Kearney, who is on the bench, Leinster also revealed that Seán O'Brien underwent "a small procedure" on his hip last Wednesday which at the least, is expected to rule him out of Ireland's opening Six Nations games against France and Italy. Leo Cullen said O'Brien would "hopefully" be back for Ireland's round three game at home to Wales on February 24th.

As for Larmour's eye-catching selection, Isa Nacewa said: "We leave all the selection thoughts to the coaches but, yeah, Jordan is just fun to play with and he is playing well. He wasn't here during the successful times of Leinster's past and I think that's a good thing because he doesn't have any boundaries in the way he thinks. He is getting out there, enjoying himself, and playing his style of rugby and he has played bloody well and we just feed off that, leave the selection to the big dogs and then we just get on with it."

New signing James Lowe has also been handed his European debut, while Nacewa comes into midfield, with Robbie Henshaw shifting to outside centre. Luke McGrath and Johnny Sexton are restored at half-back, Sean Cronin replaces the injured James Tracy, and Josh van der Flier is restored to openside, as is Cian Healy after serving his suspension, albeit to the bench along with Brian Byrne, James Ryan and Dan Leavy.

Johann van Graan has restored Stephen Archer, Billy Holland, Peter O'Mahony and Chris Cloete to an otherwise unchanged Munster side for their daunting assignment against an unchanged Racing, even without Dan Carter, in the Parisian's futuristic U Arena.

Victory would secure Munster first place in Pool Four and quarter-final qualification for a 17th time, while a bonus point defeat – provided they deny Racing a bonus point – would at least retain leadership of the group going into their final game at home to Castres next Sunday. Alternatively, were Munster to lose without a bonus point, Racing would overtake them in first place, while Castres could remain in contention by beating Leicester at home in the weekend’s finale tomorrow evening.

Last home match

Ulster are first in action when hosting La Rochelle at the Kingspan Stadium at 1pm today, and could finish the day in first, second or third place. Victory would see them usurp the French debutants atop Pool One ahead of Ulster’s final match away to Wasps, but defeat could see well them drop to third given Wasps are likely to complete the double over winless Harlequins later today.

Craig Gilroy and Louis Ludik return after missing last weekend's defeat away to Leinster, with John Cooney also reunited at half-back with Christian Lealiifano, who will be playing his last home match for Ulster before returning to the Brumbies later this month.

Alan O'Connor and Nick Timoney have been restored to the pack, while the 20-year-old Irish Under-20 World Cup final outhalf Johnny McPhillips could make his European debut after being included among the replacements.

La Rochelle, ominously, come locked and fully loaded, with their fine centre, Geoffrey Doumayrou, half-backs Jérémy Sinzelle and Alexi Bales, front-rower Dany Priso, Pierre Bourgarit and Uini Atonio, captain Jason Eaton and the outstanding Victor Vito all restored from the team which drew 38-all last week in Oyannax.

The holders Saracens face a make-or-break tie away to the Ospreys this evening, while Connacht coach Kieran Keane has recalled Irish Internationals Ultan Dillane, Bundee Aki and Kieran Marmion for their game against Worcester Warriors today (kick-off 3pm). A win for Connacht will secure top spot in Pool Five of the competition and a place in the quarter-finals with a game to spare.

Tom Farrell, Dave Heffernan and Eoghan Masterson all return after being rested last week, while Marmion returns to partner Craig Ronaldson, as Jack Carty is rested after a hectic Christmas schedule. So too are Matt Healy and Tom McCartney.

Forwards coach Jimmy Duffy said they were "well aware of the threat posed by Worcester" but added: "We are targeting a home quarter-final, which would be a massive occasion in the Sportsground. We have two games left in the pool stages and we need to win both to be guaranteed that home quarter final."