Roberts said a recent scan revealed the damage. He noted that the latest development "hasn't really changed the course of his timetable," but didn't provide a potential return date.
Bellinger has been out of the lineup since April 5 with what was initially diagnosed as a bruised calf.
"I can say comfortably that it's not a day-to-day thing," Roberts told reporters before the Dodgers' series opener against the San Diego Padres on Friday night. "We can kind of just put it on the backburner, let Cody do his rehab and join us hopefully soon."
Bellinger sustained the leg injury when Oakland Athletics reliever Reymin Guduan spiked him in a race to first base during the ninth inning of the Dodgers' 10-3 win over the A's on April 5.
The 25-year-old Bellinger was trying to beat out an infield single when Guduan stepped on his leg. Bellinger limped off the field, but initial tests didn't reveal any structural damage in his leg.
Roberts was encouraged with Bellinger's progress earlier this week, but the Dodgers manager said the 2019 National League MVP recently "plateaued," which prompted the follow-up tests.
"He's just rehabbing daily and doing everything he can to join us as soon as possible," Roberts said.
In four games this season, Bellinger has recorded a .211 batting average with two RBIs. The two-time MLB All-Star was placed on the 10-day injured list April 9. The move was retroactive to April 6.