Shepherd was set to join the Saints before his contract was terminated because of an ankle injury.
Agent Nick Fordham said the player was left "appalled at the behaviour of Northampton in respect of the manner in which his client and family were treated".
The former Western Force man was not notified of the situation until one month after the medical, and reports are now suggesting that Shepherd will pursue legal action against the club.
"Expert medical reports from leading independent orthopaedic surgeons and Cameron's former club doctors at the Western Force have concluded that there is nothing wrong with Cameron's ankle," added Fordham.
Following the collapse of the Saints move, Shepherd is now expected to join up with the Sale Sharks.