The Pelicans traveled to New York to take on the Knicks on Friday, but Williamson did not make the trip. The team said Williamson will stay in New Orleans to undergo further testing.
No timetable for a return was given.
Williamson has appeared in all four of the Pelicans' preseason games, averaging 23.3 points and 6.5 rebounds while playing 27.3 minutes.
In summer league, Williamson played only eight minutes for the Pelicans after suffering a minor left knee bruise. The team shut him down after the first game for precautionary measures.
Williamson hadn't missed any time in training camp and was seen walking around Pelicans practice on Wednesday afternoon.
While at Duke last season, Williamson suffered a mild right knee sprain when his sneaker gave out seconds into a game against North Carolina. He missed six games total.
New Orleans opens the regular season Tuesday in Toronto against the defending champs.