The Milwaukee Bucks have been fined $50,000 after Jon Horst promised Giannis Antetokounmpo would be offered a supermax deal next year, the NBA has confirmed.

Bucks general manager Horst said NBA MVP Antetokounmpo would be offered a five-year, $250million deal following the 2019-20 season.

Horst publicly discussed Milwaukee's plans for the Greek's contract at a fan town hall meeting in a violation of the league's ruled governing the timing of discussing player deals.

"Under NBA rules, teams cannot commit to offer a 'supermax' extension before the summer following a player's seventh season in the NBA," the league said in a statement announcing the fine.

Antetokounmpo, who turns 25 in December, will be a free agent in 2021 if he does not sign the contract extension in 2020, making him one of the most coveted players on the market.

The Bucks superstar is playing on a four-year, $100m deal he signed before the 2017-18 season.

In 72 games last season, his sixth in the NBA, Antetokounmpo averaged 27.7 points with 12.5 rebound and 5.9 assists, collected the MVP award and earned his third All-Star selection.