Dallas declined its $5 million team option on Nowitzki to create more flexibility in free agency, thus making him an unrestricted free agent.
Nowitzki has spent his entire 20-year NBA career with the Mavs, and the 40-year-old seemingly doesn't have much time left as an active player.
The German star appeared in 77 games last season, but he averaged just 12.0 points and 5.7 rebounds per game, which were his lowest marks since his rookie campaign in 1998-99.
Nowitzki remained efficient, though, as he shot 45.6 percent from the field and 40.9 percent from three-point range.
During an interview with Mavs.com in May, Nowitzki suggested that it's possible he will continue playing beyond the 2018-19 season.
If he does so, he will become the first player in NBA history to play 22 or more seasons.
Provided he re-signs with Dallas, Nowitzki will become the only player to spend 21 seasons with the same team, breaking a tie with Los Angeles Lakers legend Kobe Bryant.
After declining Nowitzki's option, the Mavs reportedly came to terms with free-agent center DeAndre Jordan on a one-year deal, according to Marc Stein of the New York Times.
That move should go a long way toward strengthening Dallas' frontcourt and giving Nowitzki some support.
Nowitzki is sixth in NBA history with 31,187 points, and he is a 13-time All-Star, one-time regular-season MVP, one-time NBA champion and one-time NBA Finals MVP.
All of that adds up to a Hall of Fame career, but every indication is that he still has a love for the game that keeps him coming back.
The Mavs went just 24-58 last season, but if Nowitzki returns and Jordan signs, then Dallas could potentially get itself back in the playoff mix next season provided guard Dennis Smith Jr. continues to improve and 2018 first-round pick Luka Doncic is as good as advertised.