"Realistically it's eight weeks," Gibson said. "So he's done."
Although he will avoid surgery, with almost exactly eight weeks left in the season, the chances of last year's National League MVP runner-up returning this season are slim after being placed on the disabled list on Saturday.
"If you rush it, then you end up injuring it and you displace the fracture," Gibson said. "I think you're looking at worse things."
Goldschmidt's injury is the latest and largest blow to the D-backs, who have been racked by injuries all season.
The team currently has 10 players on the DL, including five pitchers who underwent Tommy John surgery. One of those injured players, outfielder A.J. Pollock, is working his way back from a fractured right hand caused by another hit-by-pitch.
Before the injury, Goldschmidt was leading the team in nearly every meaningful offensive category, including doubles, home runs, RBIs and wins above replacement (WAR).
"If you just look at Goldy, he counts for over 30 percent of our run production," Gibson said.
Adam Lichtenstein is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.