Williams left practice Sunday with his right arm hanging, Rapoport adds. His return timetable reportedly has yet to be determined.
The 25-year-old led the NFL with 20.4 yards per catch last year and racked up career highs of 49 receptions and 1,001 yards through 15 games. He also scored two touchdowns.
The Chargers picked up the fifth-year option on Williams' rookie contract this offseason. He was selected seventh overall in 2017 after a decorated career at Clemson.