Seibold has yet to re-sign with the Rabbitohs beyond the 2019 season as he is in contention to replace Wayne Bennett at the Broncos in 2020.
The Rabbitohs have given Seibold until the end of the month to re-sign with the club. Should he decline, his position would be untenable and he could be replaced by Furner.
Furner is currently an assistant coach at the Rabbitohs. He previously coached Canberra between 2009 to 2013.
The former Canberra forward was recently appointed coach of Leeds but has a get-out clause in his deal.