No date for the surgery has been set. A timetable for his return will be established once he has the procedure.
The Blazers say Williams tore the tendon Tuesday during a voluntary workout at the team's practice facility.
Williams missed his rookie season in 2010-11 after surgery on both knees. Last season, he averaged 3.7 points in 24 games before a shoulder injury that required surgery on March 30.
The 6-foot-5, 183-pound guard was the 22nd overall pick of the 2010 draft out of Memphis.