Walker appeared in two games for the Celtics this season, scoring two points in six minutes . In seven preseason games with Boston, he averaged 3.9 points and 2.4 rebounds in 12.3 minutes.
Selected in the second round of the draft with the 47th overall pick by the Washington Wizards, Walker was acquired by Boston on June 28.
In two years at Kansas State, Walker averaged 15.3 points and six rebounds in 26.6 minutes. He earned third-team All-Big 12 honors as a redshirt freshman in 2007-08.
Walker, the season's sixth player to be assigned to an NBA D-League affiliate, is expected to join the Flash later Friday. He will likely play in Saturday's preseason game against the Idaho Stampede in Burley, Idaho.
The Flash are also affiliated with the Utah Jazz.