Lleyton Hewitt has launched a defamation action against the Association of Tennis Professionals, the governing body of the men's game.
The 22-year-old Australian, who lost his world No 1 ranking to Andre Agassi last week, is suing the ATP for $1.5m (£890,000), claiming that he was unfairly fined for failing to appear for a US television interview before a tournament in Cincinnati last August.
Hewitt was fined $106,000 by the ATP for allegedly failing to fulfill his TV commitments on 6 August. The fine was reduced to $20,000 on appeal on 14 January and Hewitt maintains he was prepared to do the interview after he had been informed of the possible fine. He said the ATP had unlawfully withheld half his prize money at Cincinnati.
Hewitt announced his intention to sue last month, saying it could only be avoided if the ATP made a public apology and admitted that the fine had been wrongly imposed. The ATP refused.