European Cup: Gerry Thornley on how the fate of so many teams hangs in the balance over the next two weeks

It's back, and not a moment too soon. The opening salvos in the Heineken European Cup have lent the tournament a certain fluidity but traditionally, the third and fourth rounds of back-to-back fixtures sort out much of the wheat from the chaff and by Sunday week the tables will start to tell a few truths.

Thus far, only four clubs have come through the opening two rounds with a brace of victories. Sale Sharks, Perpignan, Saracens and Bath Rugby are the four to remain unscathed, the Sharks, Perpignan and Bath each picking up a try bonus point as well to put down early group markers.

Even so, Sale have still to travel to what would seem their most difficult away assignments: Castres this Friday and Thomond Park on the final weekend of pool matches.

And likewise so do Perpignan, though admittedly their main opposition in Pool Two is provided by Leeds and Cardiff.

At the other end of the scale, the Dragons, Calvisano, Treviso and Glasgow have lost both games to date, and history has shown us that no team has ever lost the opening two matches and reached the quarter-finals.

Two knockdowns and you're counted out of the Cup, and this quartet don't look like the types to prove the exceptions.

That said, the Dragons and Glasgow have each turned a corner with a couple of wins in recent weeks.

The Welsh outfit have also lost the tournament's leading try scorer, Gareth Wyatt (whose strike rate over the last two seasons in the Cup is an impressive five tries in eight games), because of a dislocated elbow in their meaningless Powergen Cup win last weekend, but they'll have all their big guns back in their strongest-looking pack to date for the visit of Munster.

As that's in Newport, they are unlikely to relinquish all interest just yet. Furthermore, Sale's bonus-point win in round two at Rodney Parade - possibly the pick of the away wins to date this season - has raised the stakes for Munster if they are to keep the Premiership's form team within range for the last-day rendezvous in Limerick. And the European Cup is made by days like that.

Likewise, Leinster will be hoping that Glasgow's thrashing of Edinburgh last Saturday will signal an improved effort from them for their back-to-back meetings with Pool Five leaders Bath.

All in all then, the cliché about there being no easy matches - at this juncture anyhow - mightn't be too wide of the mark.

In truth, with all three Irish provinces having suffered one defeat already, they have little room for manoeuvre and are virtually in knockout mode already.

Leinster have taken the biggest hit, given they lost frustratingly and unluckily at home to Bath on the opening weekend, and most probably will have to keep winning, right up to and including their final day trek to the Rec, if they are to progress.

Certainly they cannot afford another defeat at the RDS this Saturday to Bourgoin, who daren't take as laissez faire an attitude this Saturday as they did last year when losing 92-17 to Leinster at Lansdowne Road.

Their director of rugby, Pierre Raschi, has vowed, "Our game against Leinster is very important to us - but not because we want revenge. We are very aware of the fact that our poor performances in the last few seasons have given us a reputation of being cheats and spoiling things."

Nevertheless, as things stand it's worth repeating that Leinster are the leading second-placed side in the tournament.

In reality, the tables have taken shape pretty much along expected lines.

In time-honoured fashion, in fact even more so than before, home wins have outnumbered away wins by 18 to five. This has seen typically desultory away defeats for Biarritz and Stade Francais at Saracens and the Ospreys, and while Edinburgh's Murrayfield win over Wasps and Ian McGeechan may have raised the most eyebrows, they did scalp Toulouse at home two years ago, something the French aristocrats and holders will be mindful of this Saturday.

As expected, Pool Three was quickly labelled 'the pool of death' and sure enough just two points separate the four sides, with former double champions Leicester Tigers one point ahead of French challengers ASM Clermont Auvergne and Stade Français Paris.

Whoever emerges from that little lot will most probably need a lifejacket alright, and most likely there'll only be one between them.