Bellinger has been out since April 5 with what was originally diagnosed as a bruised calf. Roberts said the latest development "hasn't really changed the course of his timetable" but didn't want to speculate on a potential return date.
Earlier, Roberts told MLB Network that Bellinger might return in a week or two.
"I can say comfortably that it's not a day-to-day thing," Roberts told reporters before the opener of a weekend series against the division-rival San Diego Padres. "We can kind of just put it on the backburner, let Cody do his rehab and join us hopefully soon."
Bellinger sustained the injury when Oakland Athletics reliever Reymin Guduan stepped on his leg in a race to first base in the ninth inning of an eventual lopsided victory by the Dodgers. Bellinger limped off the field, but initial tests didn't reveal any structural damage.
Roberts expressed encouragement in Bellinger's progress earlier this week but said he recently "plateaued," prompting follow-up tests.
The course of Bellinger's rehab, which includes hitting and throwing, won't change because of the hairline fracture, Roberts said, adding: "He's just rehabbing daily and doing everything he can to join us as soon as possible."