The small forward underwent surgery during the week to remove a screw in his foot that had been causing him discomfort.
He is expected to be sidelined for around 10 weeks.
“Cory’s recovery has been steady, but these types of injuries take time to heal and fully recover,” general manager of football Steve Hocking said.
“Unfortunately Cory has been experiencing some pain and surgery was the preferred option to resolve the issue as quickly as possible.
“We expect Cory to return to light training duties in around 10 weeks.”
Gregson played 20 games in his debut season in 2015, before managing just nine last season.