The 6-foot-6, 201-pound forward was called up Tuesday from the NBA Development League, where he played for the Rio Grande Valley Vipers.
Johnson started 14 games for the Vipers this season and averaged 20.1 points, 5.9 rebounds, 2.1 assists and 1.8 steals. The 24-year old began the season with the Philadelphia 76ers and averaged 6.0 points, 2.9 rebounds and 1.0 steals in nine games.
Johnson has played 57 NBA games between the 76ers, Boston Celtics and Memphis Grizzlies since 2012-13. He's played in 73 development league games, was a 2014 all-star and a member of the league champion Vipers in 2013.