The tennis coach who began working with Naomi Osaka back when she was 13 claims her father signed a contract promising him 20% of her career earnings ... and now he's coming to collect.
The man behind the lawsuit is Christophe Jean -- who says Naomi's father, Leonard Francois, hired him to work with Naomi and his other daughter, Mari, back in 2011.
Jean says Francois couldn't pay his rates 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.