Europe's elite begin their Heineken Champions Cup campaigns this weekend.
A lot of attention will be focused on holders Saracens, who were docked 35 points for breaching the Premiership Rugby salary cap, when they face Racing 92 in Paris on Sunday.
Competition organisers are concerned Saracens will be more concerned about overcoming their domestic penalty than performing well in Europe.
"Perhaps other clubs will be happy that they are going to be a bit wounded but it's not good news for us," said Vincent Gaillard, director-general of European Professional Club Rugby.
On top of their points deduction, Saracens face an additional fine of more than £5m if any appeal against a penalty for breaching the salary cap is not successful.
Saracens director of rugby Mark McCall has said the club will "expose some younger players to European rugby over the course of the season" to "accelerate their development".
Gaillard says he "would prefer that they are thoroughly behind the competition".
"Our concern rests in their capacity to put everything into the European Cup knowing that they will have to fight all the way to avoid relegation," he added.
|European Champions Cup final wins|
|4: Toulouse, Leinster|
|3: Saracens, Toulon|
|2: Leicester, Munster, Wasps|
|1: Brive, Northampton, Ulster, Bath|
After six rounds of games, five pool winners and the three best runners-up will qualify for the knock-out stages.
The final takes place in Marseille on 23 May.
Four-time European champions and Pro14 winners Leinster face Lyon, Northampton and Benetton in Pool One.
Last year's beaten finalists will be out to avenge that defeat by Saracens as they begin their tournament against Italian side Benetton on Saturday.
Scrum-half Luke McGrath said this week he hopes Leinster, coached by former England boss Stuart Lancaster, can emulate Japan's performances at the World Cup after witnessing the hosts beat Ireland.
"The Japanese skill levels were incredible and the speed that they were playing at," said McGrath. "Hopefully we can do something similar."
Northampton get their campaign under way against Lyon the following day, fresh from the news that former captain and hooker Dylan Hartley has retired from rugby.
Premiership runners-up Exeter come up against Glasgow Warriors, Sale Sharks and La Rochelle.
It will mean a return to face his former club for Exeter's new signing Stuart Hogg, but first the Chiefs travel to La Rochelle on Saturday.
Exeter back Henry Slade has already been back in action for his club side after playing for England in the World Cup final loss to South Africa two weeks ago.
Slade could come up against a man who was part of the Springboks side that inflicted a 32-12 defeat on England in the form of Sale scrum-half Faf de Klerk, while a second Bok who started the final, new Sale lock Lood de Jager, is out for up to six months with a dislocated shoulder.
The Sharks, who visit Glasgow on Saturday, have been drawn in the same pool as French outfit La Rochelle, who beat them in last season's Challenge Cup semi-final.
Harlequins are the only team in this Pool Three not to have reached the top European final, as they go up against 1998 winners Bath, 1999 champions Ulster and three-time runners-up Clermont Auvergne.
Kyle Sinckler saw his World Cup final cut short by a head injury inside two minutes, but the England prop was recently called the "best tight-head in the world" by team-mate Danny Care.
Sinckler and scrum-half Care, who missed out on a surprise late call-up for the final himself when Eddie Jones opted for Ben Spencer to replaced the injured Willi Heinz, will be hoping Quins' form in Europe is better than their domestic showing - they have recorded just one win in their opening four Premiership games.
They visit a Clermont side on Saturday boasting the likes of France centres Wesley Fofana and Damian Penaud, veteran Scotland scrum-half Greig Laidlaw and France lock Sebastien Vahaamahina, who was sent off against Wales in the World Cup quarter-final.
Elsewhere, Ulster head to Bath, with former fly-half Ian Humphreys saying it could be vital to their hopes that they only had Iain Henderson and Jacob Stockdale at the World Cup.
"I'm massively confident they can make it through the pool," Humphreys told BBC Radio Ulster.
European and Premiership champions Saracens will meet two-time winners Munster, French giants Racing 92 and Welsh side Ospreys in a tough Pool Four.
Saracens back Alex Lozowski is confident the club - aiming to win a fourth Champions Cup in five years - will challenge again, if not in the immediate future.
"Maybe not this season, but we will win championships again and I want to be part of that and we all want to be a part of that," said Lozowski.
However, Racing 92 lock Dominic Bird remains wary of the holders' visit to Paris this weekend.
"I have no doubt it will be a very good second team," said the former New Zealand international.
"All I care about is that we will come up against one of the best sides, if not the best side, in Europe this weekend and I'm excited about that challenge."
The French outfit will be without Fiji second-row Leone Nakarawa after he was suspended for returning from the World Cup late.
Meanwhile, Ospreys will hope to recover from a run of five defeats in six games when they host Munster on Saturday, with coach Allen Clarke calling it a "dark period" for the club.
Gloucester get the tournament under way on Friday when they host Top 14 winners Toulouse, who are looking for a record fifth Champions Cup.
The French outfit have not won the competition since 2010 but boast an exciting team that includes World Cup-winning Springbok wing Cheslin Kolbe, who scored a try in the final against England.
Also in the Toulouse ranks are the young French half-back pairing of Antoine Dupoint, who will miss the game at Kingsholm, and number 10 Romain Ntamack.
Connacht have a number of injury concerns heading into their opening fixture against Montpellier on Sunday, with Ireland under-20 second row Sean O'Brien among those missing.
Champions Cup round one
Friday 15 November
Gloucester v Toulouse (19:45 GMT)
Saturday 16 November
Bath v Ulster (13:00 GMT)
Glasgow v Sale (13:00 GMT)
Leinster v Benetton (15:15 GMT)
La Rochelle v Exeter (16:15 GMT)
Ospreys v Munster (17:30 GMT)
Clermont v Harlequins (18:30 GMT)
Sunday 17 November
Northampton v Lyon (13:00 GMT)
Connacht v Montpellier (13:00 GMT)
Racing 92 v Saracens (16:15 GMT)