Williams is listed on the team's official injury report as day to day. His calf has been bothering him after he aggravated it in the All-Star Game, and he re-injured it in the second quarter of Friday night's win in Charlotte, forcing him to leave the game.
Backup Jordan Farmar will start in Williams' place.
"Right now, he's pretty much about the same that he was the last game, so he's day to day, game to game," Nets coach Avery Johnson said after his team's Monday morning shootaround. "We'll have another update for you Tuesday, and we'll continue to treat him.
"But this is a guy that just doesn't miss games, so if he's missing games, he's definitely injured."
The Nets are hopeful that Williams can return for Wednesday night's game against the Toronto Raptors, but nothing is certain at this point.
In 40 games, Williams is averaging team highs of 22.1 points and 8.1 assists for the Nets (14-28), who are 4½ games behind the New York Knicks for the eighth and final playoff spot in the Eastern Conference.
Mike Mazzeo is a regular contributor to ESPNNewYork.com.