The Rockets assigned Whitmore to the G League's Rio Grande Valley Vipers on Thursday, Vanessa Richardson of Space City Home Network reports.
Whitmore has struggled to carve out a significant role to begin the season, and in the club's last four games, he's seen the floor just three times while averaging 4.7 points and 1.3 rebounds across only 6.7 minutes per game. The 20-year-old isn't expected to spend much time with Rio Grande Valley, though it will likely take an injury to one of Houston's rotation players before he gets meaningful run at the NBA level.