Dvorak had been working his way back from a lower-body injury when he tore a pectoral muscle during a rehabilitation skate – with him requiring surgery Friday.
This leaves him with the real possibility that he will not play at all in the 2018/19 season, a huge loss for a Coyotes team that needs more goalscoring.
The Coyotes (2-4-0) have been without Dvorak, Alex Galchenyuk and Jakob Chychrun so far this season but it looked as if the trio had finally turned a corner in their respective recoveries.
But now, the 22-year-old that has 70 points (30 goals, 40 assists) in 156 regular season games since joining the Coyotes, looks set to be out for many months.