The 26-year-old declined his $3.8 million player option for the 2021-22 season on Saturday, agent Mark Bartelstein told ESPN's Adrian Wojnarowski.
The Bucks signed Portis to a two-year, $7.4 million deal in November. He was trying to reestablish himself after a failed start to his career with the Chicago Bulls and playing for three different teams in the previous two years.
Playing primarily a scoring role off the bench for head coach Mike Budenholzer, the Arkansas product was able to maximize his skills to great effect. He averaged 11.4 points, 7.1 rebounds per game and set career-highs with a 52.3 field-goal percentage and 47.1 three-point percentage.
Portis ranked second on the Bucks in rebound average, behind Giannis Antetokounmpo (11.0), despite playing only 20.8 minutes per game.
Scoring has been his primary asset dating back to his college days with the Razorbacks, and he has carved out a valuable role in the NBA as a role player off the bench.
Given his versatility as a scorer and rebounder, Portis could be one of the most sought-after role players on the market this summer.