The Grizzlies announced the deal Wednesday.
The 6-foot-6 Johnson had been averaging 12.6 points, 4 rebounds and 1.81 steals in 21 games with the Rio Grande Valley Vipers of the NBA's Development League. He ranks fourth in the D-League with 54 3-pointers made and tied for sixth with 38 steals. He played four years in college at Dayton and was the 2010 National Invitation Tournament MVP in helping the Flyers to the title game.
Johnson played for the Clippers and Orlando in the preseason.
The move leaves the Grizzlies with 12 players on the roster.