That move could now be under some doubt, with The Age's Sam McClure reporting Casboult remains unvaccinated as he awaits the arrival of the Novavax vaccine from the United States.
Casboult will need to be fully vaccinated in order to play next season, however Queensland players aren't required to have their first dose until January 21.
Novavax however isn't TGA approved in Australia, meaning Casboult's wait faces an unclear timeline ahead of the upcoming season.
7 News' Mitch Cleary reports that Casboult has previously suggested he would be open to receiving the Pfizer or AstraZeneca vaccinations, which are currently available in Australia.
Levi Casboult is poised to join GC as a rookie next Fri. He’s not yet vaccinated, has been waiting for Novavax. But has previously indicated he would get Pfizer/AZ if required. QLD/WA/SA players don’t need 1st dose til 21st Jan. Will be handy King/Chol/Day back-up @7NewsMelbourne
— Mitch Cleary (@cleary_mitch) November 15, 2021
The Suns' hopes of signing Casboult come amid their stunning call to delist Hugh Greenwood ahead of next Wednesday's National Draft, with the midfielder having backflipped on the planned strategy to join North Melbourne on a two-year deal.
Greenwood's departure opens up another list spot for the Suns to fill for 2022, with Casboult now perhaps more of a necessity than ever before.
Suns football boss Wayne Campbell opted not to speak on Casboult's vaccination stance, but confirmed contract discussions have begun.
"Have we spoken to Levi about potentially coming to the Gold Coast? Yeah we have. Over a period that will play out, whether it plays out or doesn‘t. (But) an individual player’s vaccination status, I don’t think it’s for me to go into," Campbell told 3AW.
“Levi Casboult is not a Gold Coast player at this stage … and I don’t think I should be discussing what his vaccination status is.”
Casboult played 154 games in the navy blue since making his debut in 2012, booting 156 goals during his tenure at Princes Park.
The 2021 Rookie Draft is set to take place next Friday on November 26.