Dunn, 27, is 6-foot-3 and attended training camp with the Grizzlies, but was waived before the start of the season.
Injuries limited Dunn to four games with the Hawks last season. He appeared in 51 games the year before that, averaging 7.3 points, 3.6 rebounds and 3.4 assists.
The No. 5 overall pick in the 2016 draft, Dunn spent his rookie year with the Timberwolves. He has appeared in 231 games overall, compiling career averages of 8.2 points and 4.1 assists.
The Hawks traded him to the Celtics at the end of last season, and then the Celtics traded him to the Grizzlies. He has remained an NBA free agent since being waived by Memphis.