"This decision was made because it's in the best interest of Monta," Fried said. "It was more about him taking his future into his own hands."
The Mavericks do not intend to attempt to re-sign Ellis despite the fact that he averaged 18.9 points last season to become the first player other than Dirk Nowitzki to lead them in scoring since 1999-2000.
Fried, though, did not rule out a return to Dallas for his client.
"Monta's experience in Dallas was definitely a positive one," Fried said. "The team and the organization had success and Monta grew as a player. A door to return there will always be open."
Ellis' other agent is Happy Walters.
Ellis, 29, had a Wednesday deadline to determine whether he wanted to make $8.7 million in the final season of a three-year, $25 million deal or test the free-agent market. If Ellis had picked up the option, the Mavs would have attempted to trade him for a first-round pick to clear cap space, sources told ESPN.com.
The 6-foot-3 Ellis, an undersized shooting guard who is one of the league's most dynamic off-the-dribble threats, played a key role in the Mavs' winning a total of 99 games and advancing to the playoffs in each of the past two seasons after Dallas' one-year postseason absence.
But his moodiness negatively impacted team chemistry last season, sources said.
The Mavs, who plan to use Chandler Parsons as more of a point forward in the second season of his three-year, $46 million deal, want to have a bigger shooting guard who is more of a 3-point threat than Ellis. Potential fits in free agency include Danny Green and Wesley Matthews.
Ellis, a 10-year veteran, has a career scoring average of 19.3 points per game, the highest in NBA history among players who never have been an All-Star. Ellis signed with the Mavs in the summer of 2013 after declining an $11 million player option for the final season of his previous contract and turning down a three-year, $36 million offer to remain with the Milwaukee Bucks.
Dallas didn't have the cap space to sign Ellis to the three-year, $25 million deal until discovering that Devin Harris had a serious toe injury that required surgery, prompting the Mavs to take an offer to Harris off the table and significantly increase their offer to Ellis.