ESPN's rugby predictions: Games of the week, potential upsets & more

Continental competition is back for the first time in 2018 with the quarterfinal line-up in both the Champions and Challenge Cups to be finalised over the next fortnight.

ESPN's experts predict which teams are set for a big weekend, which players will shine and where your attention should be trained across the two competitions.

Player to watch

Champions Cup (Martyn Thomas): Billy Vunipola (Saracens). Mark McCall's Saracens face a make-or-break clash with Ospreys as they take their fragile hopes of making the knockout stages to South Wales. If Vunipola can have the kind of impact at the Liberty Stadium that he did on his return from injury at Wasps last weekend then Saracens may well maintain a challenge for the quarterfinals into the final weekend of pool play. The England No. 8 was at his abrasive best in Coventry as McCall's side secured an impressive 38-15 win. They'll need more of the same in Swansea.

Challenge Cup (James Harrington): Jake Polledri (Gloucester). It has been a tremendous week for the young flanker, who was named among Italy's initial 34-player squad for the Six Nations. What better way to wrap it up than with a big performance at Agen as the West Country side look to keep up the pressure on current Pool 3 leaders Pau? Defeat for the Cherry and Whites, however, would leave the door open for Simon Mannix's Top 14 side to book a quarterfinal berth against Zebre nearly 24 hours later.

Game of the weekend

Champions Cup: Racing vs. Munster, Sunday, 3.15 p.m.

First versus second in Pool 4 go head-to-head at the U Arena, as Munster chase the victory that would secure their passage to the quarterfinals. Munster edged the return fixture -- that remarkably remained scoreless for an hour -- thanks in no small part to Conor Murray's charge-down try. With Racing determined to keep their qualification hopes intact going into the final week expect this encounter to be just as close. It should be an emotional occasion too as Munster return to Paris for the first time since Anthony Foley's death.

Challenge Cup: Bordeaux vs. Dragons, Saturday, 8 p.m.

The battle of the Pool 1 sides locked together on 11 points should be a cracker. Top slot is almost certainly out of their reach -- Newcastle should beat Enisei-STM at Kingston Park to tie-up a home quarterfinal. On the other hand, one of the three remaining last eight places is still a distinct possibility. But maximum points are vital here, so expect a flood of tries.

Potential upset

Champions Cup: Ospreys vs. Saracens, Saturday, 7.45 p.m.

Defeating the back-to-back European champions is a tall order at the best of times -- especially when their backs are against the wall and their involvement in this year's competition is on the line. Yet, Ospreys have saved their best form this season for the continent's grandest stage. The Welsh region were unlucky to lose a 70-point try-fest at Allianz Park in October and head into this game having lost just one of their last five matches in all competitions. Saracens have hit form themselves, so it promises to be another cracker.

Challenge Cup: Edinburgh vs. Stade Francais, Friday, 7.35 p.m.

Friday's meeting at Murrayfield could equally be the game of the weekend -- as Richard Cockerill's Edinburgh pit their perfect 20-point record against Greg Cooper's revitalised defending champions. A win for the hosts would ensure a home quarter-final, but Stade won't give up their title without a fight. One thing's for sure, the Paris side know how to duke their way to the final. They did it the hard way last year, qualifying as the eighth-ranked side.

Big weekend for...

Champions Cup: There are huge ties across all five pools -- starting with the Scarlets' trip to Bath Friday night -- as Wasps, Ulster, Exeter, Montpellier, Toulon and the whole of Pool 4 battles to stay on the road to Bilbao. But perhaps the team with most to lose is Saracens. The defending champions have been left scrapping for a place in the last eight following a woeful run of form in late November and early December that culminated in back-to-back defeats to Clermont. Barring a huge upset, the French side will secure the win over Northampton that should wrap up Pool 2, meaning Saracens must beat Ospreys to have any hope of joining them in the knockout rounds.

Challenge Cup: John Muldoon. The Connacht captain is set to make his 50th Challenge Cup appearance against Worcester at Sixways as the Pool 5 leaders look for the win that would make sure of a quarterfinal place for the ninth time. It won't be easy -- the Warriors still have a chance of qualification themselves -- but, as well as Muldoon, the PRO14 side have an ace in the hole in this season's top-scorer Jack Carty, who has notched up 53 points in the opening four rounds.