Johnson, 22, started 74 games for the Spurs in his third season, averaging a career-high 17.1 points and shooting 39.8 percent from 3-point range.
Friday’s deal comes two weeks after the Spurs traded the All-Star guard. Dejounte Murray to the Atlanta Hawks in the future Danilo Gallinari and three first round picks. Mary led the Spurs with 21 points per game last season.
Johnson was the Spurs’ first-round pick in the 2019 draft, going No. 29 overall.