Castle is out for Friday's game against the Trail Blazers due to a left shoulder contusion, Paul Garcia of ProjectSpurs.com reports.
Castle banged his shoulder in the second quarter of the 121-116 win over the Pelicans on Dec. 8, a game in which he finished with 22 points, five rebounds and four assists across 34 minutes. Even though the early diagnosis was just a bruise, the rookie will receive some extra rest and will sit out Friday's rematch against Portland. His next chance to play will come against the Timberwolves on Sunday.