Warren Gatland has been warned that Toulon will refuse to release Gethin Jenkins or any other players for the start of the British and Irish Lions tour if they reach the Top 14 final.
Gatland, who was unveiled as Lions head coach this week, has travelled to France for talks over the release of French-based players for the tour of Australia next summer.
The Lions open their 10-match tour against the Barbarians in Hong Kong on June 1, the same day as the Top 14 final.
And Toulon coach Bernard Laporte told L'Equipe: "The international window begins on the weekend of June 9. Everything that happens before that is outside of the window.
"As far as freeing up Gethin, in principle, it's a no.
"If he plays in the final, he will leave the day after, on Sunday June 2, but not before.
"We won't pay a player who has to go and play for the Lions at the most important time of our season.
"There is no specific clause in his contract about it."