It is unclear whether Williamson will miss more than one game.
"He had inconclusive (COVID-19 test) results and the timing became a factor," coach Stan Van Gundy said. "He's not with us here at the game tonight. He's back in his hotel room. We'll know more as further results come back."
The Pelicans traveled to Los Angeles on Tuesday after they were supposed to start a seven-game, 13-day road trip in Dallas on Monday. However, that game was postponed because of positive COVID-19 cases and contact tracing with the Mavericks.
The Pelicans were already set to be without Lonzo Ball (bilateral knee tendinopathy) before also ruling out Eric Bledsoe (right eye irritation) on Wednesday. JJ Redick is listed as probable (right hamstring tightness).
Williamson is averaging 21.9 points on 55.7% shooting and 8.1 rebounds in nine games. This is the first game he will miss this season.