He's expected to command interest from multiple suitors, Haynes adds.
Powell stood to earn just over $10.2 million next season after signing a four-year, $37-million deal with Dallas back in 2016.
The 27-year-old scored a career-best 10.6 points per game this past season. He also averaged 5.3 rebounds and 1.5 assists in 21.6 minutes per contest.
Powell was a second-round pick of the Charlotte Hornets in 2014, but his rights were quickly traded to the Cleveland Cavaliers less than a month after the draft. He was on the move again before the start of the season as the Cavaliers traded him to the Boston Celtics in September. Boston then shipped him to Dallas along with Rajon Rondo the following December.