The injury occurred Tuesday night in the seventh inning against the Pittsburgh Pirates, when he collided with the outfield wall. Toles was hurt trying to catch Andrew McCutchen's ground-rule double to left field that ended Dodgers starter Julio Urias' no-hit bid.
X-rays were negative, and Toles underwent an MRI exam on Wednesday, which revealed the extent of the damage.
The 24-year-old was batting .271 with five home runs and 15 RBIs in 31 games this season. He made his major league debut on July 8, 2016, and he hit .314 with three home runs and 16 RBIs in 48 games last year.
Toles is expected to have the knee operation in seven to 10 days.