Guernsey FA chairman Mark Le Tissier says the island's existing clubs must remain attractive to local players if they do not want to lose them.
Local sides are unhappy at the approval of a new team aiming to play in the Kent Premier League next season.
They fear the best players will leave and the game on the island will suffer.
"They have to ensure that the product and the things they offer at their club are enough to keep their best players," Le Tissier told BBC Guernsey.
"They now have a rival and have competition for their players and they have to meet that competition.
"Players, at the end of the day, will make their choice as to where they go and play their football.
"It's up to our member clubs that are in existence at the moment to make sure they keep them."
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