Middleton is one of three Bucks' starters entering free agency, joining Malcolm Brogdon and Brook Lopez.
Bucks forward Khris Middleton declined his $13 million player option for 2019-20 on Wednesday and will now become an unrestricted free agent, according to ESPN's Adrian Wojnarowski.
The 27-year-old earned his first All-Star appearance in 2018-19 with 18.3 points per game on 37.8% shooting from three. Middleton was Milwaukee's No. 2 scorer last season behind potential MVP Giannis Antetokounmpo.
Middleton declined his option on Wednesday, but that doesn't necessarily portend a departure from Milwaukee. The Bucks and Middleton are "planning to work together toward a new long-term deal," per Wojnarowski.
Middleton can sign a five-year, $190 million deal with Milwaukee, with a maximum contract of four-years, $140 million available from any other team. Middleton previously signed a five-year, $70 million deal with the Bucks before the 2015-16 season.
The Bucks entered the 2019 playoffs with the league's best record at 60–22. They lost to the Raptors in six games in the Eastern Conference finals.