Williams had an MRI earlier in the day and was diagnosed with a fracture of the cartilage portion of the left 12th rib. He will be re-assessed in a week, the team said.
The 30-year-old originally sustained the injury on Sunday and then sat out of Monday's game. He played on Wednesday night and re-aggravated the injury, according to ESPN.
"Deron reported some soreness above this area over the weekend and as a result underwent imaging studies on Monday, which were negative," said Nets medical director Dr. Riley Williams III. "Yesterday during the game he reported a new onset of symptoms below the prior area of soreness. New imaging studies done today demonstrated the fracture. There is no timetable for his return."
Williams is averaging 13.9 points, 6.3 assists and 3.0 rebounds in 32 games this season. He has made 25 starts and ranks 14th in the league in assists.
The Nets are 16-19 on the season and host the Philadelphia 76ers on Friday night.
- Molly Geary