Head coach Alvin Gentry believes Williamson suffered the injury during last week's preseason affair against the San Antonio Spurs.
Williamson was ruled out of the club's final preseason game over the weekend due to right knee soreness and missed the majority of summer league play with a bruised left knee.
Williamson's knee problems date back to his lone collegiate season at Duke; he missed six games for the Blue Devils after suffering a Grade 1 right knee sprain during a regular-season matchup against rival North Carolina.
The No. 1 overall pick earned the John R. Wooden Award as the nation's top male collegiate player last season. He's lived up to his billing thus far in NBA preseason play, averaging 23.3 points on 71.4% shooting while adding 6.5 boards and 2.3 assists per contest.