Tennis superstar Naomi Osaka is being sued by a former coach who says he is entitled to 20% of his former clients winnings, for life.

Christophe Jean, claims he was hired by Osaka’s father, Leonard Francois in 2011 to work with Naomi and her sister Mari.

According to a report originally published by TMZ, the tennis coach who began working with Naomi Osaka when she was 13, is claiming her father signed a contract promising him 20% of her career earnings,  and now he wants Francois to make good on the promise.

Jean says Francois couldn’t pay for his services at the time, so they struck a deal in which Jean agreed to accept 20% of Naomi and Mari’s tennis prize money and endorsement deals forever.

Jean says he has a copy of the contract where Francois agrees that the term of the deal is “indefinite.” It’s included in Jean’s suit, filed in state court in Florida.

Naomi who is now 21-years-old, has blossomed into a tennis superstar, currently ranked #1 in the world.

Last year she skyrocketed to the top after beating Serena Williams at the US Open.