British and Irish Lions coach Warren Gatland has warned any France-based stars they may miss the 2013 tour to Australia if they are unavailable for the start of the 10-match trip.
The Lions face the Barbarians in Hong Kong on 1 June - the day the French Championship final takes place.
"Ultimately, it may be up to the players," said Gatland.
"Preparation is so tight. If it means players aren't available to get on the plane, it may rule them out."
Gatland heads to France on Wednesday to talk to a number of Lions contenders and their club coaches.
"You don't want to cut your nose off to spite your face in terms of making those players unavailable if they are really, really important to you," he said.
"If you have got injuries in a certain position, you might get someone out a bit later but ideally you want everyone on the plane together.
"But if it means making a really, really tough call to say someone is not available then we might have to make that call. It might be the best thing for the squad.
"We're not going to make a hard-and-fast rule, but we are capable of making tough decisions if that's what is right for the squad."
A number of Welsh players compete in France, notably Mike Phillips, Gethin Jenkins, Luke Charteris, James Hook, Lee Byrne and Huw Bennett.
Gatland says he intends to watch Hook, Charteris and Phillips in action this weekend when Perpignan take on Bayonne.
"It is a chance to meet with coaches and talk to players and talk about potential release for the Lions players," said the Kiwi.
Charteris already has a clause written into his contract that guarantees his release for all Wales training and playing commitments.
Prop Jenkins plays his rugby at Toulon, where he is a team-mate of fellow Lions Jonny Wilkinson and Andrew Sheridan.
Full-back Byrne is in his second season at Clermont Auvergne, while Bennett left the Ospreys to play for Lyon in French rugby's second tier.
Gatland hopes his players follow the example of former Scotland lock Nathan Hines, who was a member of the 2009 Lions tour to South Africa.
"In 2009, Nathan Hines left Perpignan before a final because the Lions meant so much to him as a player," said Gatland.