The robber allegedly stabbed the staff member in the arm shortly after they confronted him.
The couple allegedly fled the scene with YSL’s luxurious bag.
The staff member was taken to hospital, where he remains.
A David Jones spokesman said the store was working with police to investigate the incident.
The spokesperson said the retailer was seeing an increase in theft and violence towards workers across the country.
“This is completely unacceptable and we continue to partner with the police and have taken appropriate measures with security across our network of stores,” they said.
“For David Jones, the safety of our team members, our dealership partner’s team members and our customers is paramount.”
The rear entrance to the store will remain closed for the remainder of the day.
Detectives are investigating the stabbing, but no arrests have been made.