The Blazers are sending Houston the 16th pick in Wednesday's NBA draft and another future first-round pick, sources said. The deal can't be finalized until after Wednesday's draft.
Covington was part of the four-team, 12-player deal that brought Clint Capela to the Atlanta Hawks in February. He came from Minnesota in one of the NBA's most expansive trades in nearly 20 years, which also saw the Timberwolves acquire two first-round picks, including Houston's 2020 pick, which they moved on to the Denver Nuggets for guard Malik Beasley and forward Juan Hernangomez.
The 6-foot-7 Covington has become one of the NBA's top defenders and has averaged 12.7 points and 5.7 rebounds in his seven NBA seasons with three teams.
Ariza, 35, arrived with the Blazers in February as part of a trade with Sacramento and started every one of his 21 games for Portland, averaging 11 points, 4.8 rebounds and one steal. He shot 49% from the floor, including 40% on 3-pointers. For his career, Ariza has averaged 10.5 points, 4.8 rebounds and 2.2 assists in 16 seasons.
Ariza opted out of participating in the NBA's Florida restart of the season, committing instead to a one-month visitation window with his young son.