He is expected to undergo surgery soon.
Sefolosha did some work on the sidelines Friday night before being ruled out with what the team called a right knee sprain.
The Jazz have lost 10 of their last 13 games and 14 of their last 18, with center Rudy Gobert (knee) sitting out since December 15.
Sefolosha is well-respected in the locker room and one of the Jazz's team leaders.
Gobert has been out since December 15 with a sprained left knee, and an evaluation Saturday revealed that he'll need at least another 7-to-10 days before returning to full-speed work.
In the meantime, Utah has struggled to find any consistency on the court sitting at a 17-25 record after dropping seven out of their last 10 games including four out of their last five contests.