The 24-year-old centre’s time at the Australian NRL club has been cut short to make way for the signing of star centre Greg Inglis.
Huddersfield have been linked with a possible move for Simpson for several weeks, with head coach Nathan Brown known to be on the look-out for an experienced outside back to boost his exciting three-quarter line-up.
But it is thought a number of Super League sides have expressed an interest in the Rabbitohs ace, which could make any potential deal far from straight forward.
Simpson has spent four seasons at Souths since making his debut in 2008.
He is out of contract at the end of 2011, but the Rabbitohs have made it clear they will not stand in his way and have, therefore, granted him a release from the final year of his contract.
If Simpson were to join the Giants – they still have two overseas quota spots available – the club would then face a race against time to secure him a work permit in time for the start of the new Super League season.