Castle exited to the locker room in the second quarter of Tuesday's game against the Lakers due to an apparent back injury, Jared Weiss of The Athletic reports.
After blocking a dunk attempt from Rui Hachimura, Castle hit the floor hard and grabbed at his lower back on the way to the locker room. If the second-year guard is unable to return, Dylan Harper would likely see increased playing time the rest of the way.