Zimmerman, who is on the disabled list and has not played since May 25 due to a small labral tear, was examined by orthopedic surgeon Dr. Tim Kremchek in Cincinnati on Wednesday.
"The doctor confirmed he was to take the route of rehabbing," Acta said. "He's just going to rest pretty much and probably a month from now start swinging the bat and doing shoulder exercises."
Zimmerman, 23, still leads Washington in home runs (8) and RBIs (27) after doing so last season. He was the franchise's first-round draft pick (fourth overall) during its first season after relocating from Montreal.
"Any time you're not talking about surgery, it's better [than the alternative]," Acta said. "At the end of this rehab, if things don't work out, he will probably go back out. But the doctor seemed to think that was not necessary."