Martinez was scratched from Tuesday's lineup against the host Arizona Diamondbacks due to groin and hamstring tightness and flew back to Los Angeles for the test.
Roberts said Martinez did have an epidural injection, and while he's not expected to need a stint on the injured list, he's unlikely to return to the lineup until at least Saturday.
L.A. wraps up a series in Arizona on Wednesday night, then returns home for the start of a four-game set against the Colorado Rockies on Thursday.
Martinez, 35, is batting .260 with 25 homers and 76 RBIs in 88 games in his first season with the Dodgers. Last month, he was named an All-Star for the sixth time in his 13-year career.