World Rugby's regulation nine states clubs must release their players for test rugby, including World Cups.
The French Top 14 season will run through the duration of the Rugby World Cup, starting in September this year.
Clubs can't publicly insist their players from Pacific Island nations don't go to Japan but there have been previous instances where it has been made clear to internationals that their future employment is at risk if they choose country before club.
Steve Jackson, who'll coach Samoa at the World Cup, says he's already had players at French clubs tell him they've had to make themselves unavailable.
"Players get pressure from clubs and this is their living," Jackson told Stuff.
"So what happens is you are tearing a player between their club and country.
"It's just not fair on the players to make those decisions.
"We'd love to have them but there are certain players who won't be coming to the World Cup, purely because of those reasons."
Jackson, the former North Harbour coach, understands the predicament his players face and unlike those from richer countries, they aren't in a strong negotiating position.
"It's not because they don't want to come," Jackson said.
"But the financial benefits for them to stay and the pressure from their clubs overseas is pretty high.
"They (the clubs) don't say they do it, but they do.
"It's something that needs to be looked at, but you can't do much about it at the end of the day.
"The team that we put out on the field, is going to be a team that has things we can't coach, like passion, hunger and wanting to play for your jersey.
"The group of players we've been speaking to certainly have that, so I'm excited about the opportunity that's going to be put in front of us."
Tonga assistant coach Pita Alatini says they're also in the same position.
"That's the challenge we're always going to have, where players get offered a better contract to stay on, rather than to go to the World Cup," the former All Black said.
"That comes down to the individual and for each player around how much the jersey means to them, compared to value.
"We understand that from the point of view of a player who needs to look after his family.
"In terms of that, we have to deal with it as we go and we rely heavily on those boys.
"They know that and at the end of the day, it's their choice and we can only do so much."
Alatini says he and head coach Toutai Kefu don't know yet how many players will rule themselves out of the World Cup, but will find out soon.
"There are a couple of players who haven't made a decision yet as such," he said.
"So over the next couple of weeks, as we lead into the Pacific Nations Cup we'll get a better idea of who's committed and who's not."
For last year's tour to the northern hemisphere Jackson selected five players based in France, while there were nine Tongan players from French clubs when they toured at the same time.
Tongan players were Paul Ngauamo, Paea Faʻanunu, Siegfried Fisi'ihoi, Ben Tameifuna, Leva Fifita, Michael Faleafa, Maama Vaipulu, Daniel Kilioni and Alaska Taufa.
The Samoan players were Manu Leiataua, Paul Alo-Emile, Piula Faʻasalele, Ed Fidow and Tim Nanai-Williams.
After the 2011 Rugby World Cup in New Zealand, former Racing Metro backs coach Simon Mannix claimed that the club paid off Jone Qovu, Josh Matavesi and Sireli Bobo not to play for Fiji.
"Racing Metro had Fijians who declined to go to the World Cup ... because the club gave them a cheque if they stayed here [in Paris]," Mannix told The Independent newspaper in 2012.
The Independent also approached former Fiji first-five Nicky Little about the allegations. He has played for clubs across Europe and contested four World Cups and he confirmed shady dealings.
"For many seasons, European and UK-based Islanders have either been blackmailed not to play for their countries or had pay docked when they were with their national teams," Little told The Independent.
Despite World Rugby's attempts to stamp out the problem, it appears that once again that this World Cup will be a battle between the haves and have nots.