Muncy left Wednesday's game against the Padres with what was initially diagnosed as a wrist contusion. X-rays taken before Thursday's series opener in Arizona revealed no fracture.
Before the results of the X-rays were available, Roberts said Muncy would not return until early next week regardless of the extent of his injury, though the outcome of his tests could affect the team's plans for the September roster.
"If we get different news than the initial diagnosis [on Muncy], then, yeah, we'll probably be a little more aggressive with our September call-ups," Roberts said. "I don't really know who, but obviously you've got to replace him."
Roberts would not say if that plan could include shortstop Gavin Lux, whom ESPN's Keith Law ranked in July as the No. 5 prospect in all of baseball. Lux is hitting a combined .346 with 26 homers and 76 RBIs in 112 games at Double-A Tulsa and Triple-A Oklahoma City.
Muncy said Thursday that the injured wrist felt "pretty painful" and had limited range of motion.
"If there's a tiny crack or hairline fracture, the machine won't show it. So we're basically just double-checking it and hoping for the best," Muncy said before his X-rays. "With how it feels right now, I'm a little nervous. But I'm also just trying not to get my hope up that, 'Oh, the pictures came out negative, it's all good.' ... I'm trying to stay neutral with it right now."
Muncy, 29, who is batting .253 with 33 homers and a career-high 87 RBIs in 129 games, was a first-time All-Star this season, his second with the Dodgers. He is unlikely to be placed on the injured list because rosters expand Sunday.
Information from The Associated Press was used in this report.