Jack, who mysteriously departed the Fina world championships in South Korea just days before they began citing "personal reasons", later admitted she had failed a doping test, testing positive to Ligandrol.
Initial reports out of Sydney indicated she had already been banned, but she faces an Australian Anti-Doping Authority (Asada) hearing on Friday.
The Daily Telegraph said Jack would receive the maximum four-year penalty unless she could prove her innocence and that she did not take the drug.
The 20-year-old has asserted she did not knowingly take the drug and has vowed to clear her name.
Ligandrol is a drug popular with bodybuilders and used for repairing worn-out muscles and increasing muscle mass.
Asada has officially notified Jack of the maximum ban, the Sydney Morning Herald reported.
Her legal team is reportedly plotting a defence to prove the scenario that she did not take the drug knowingly in the hope of having her potential suspension reduced.
They will need to prove exactly how Ligandrol was found in her system, including what supplement was contaminated and by whom if they decide to pursue that path.
Jack has protested her innocence and still wanted to compete at the 2020 Olympics in Tokyo.
"Deep down, I feel I shouldn't have to defend my reputation as I know that I didn't do this," she said.
"I get tested approximately every four to six weeks so why would I take anything banned and do this to myself?
"Especially leading up to competition where I could be tested daily.
"Why would I put myself through this anguish and risk jeopardising my career and my character?
"I did not and would not cheat and will continue to fight to clear my name."
Jack had already been banned from the rich International Swimming League as she prepared to fight her doping case.
She had been included in the Cali Condors team for the ISL's series starting this October, but organisers said she was suspended from the league, pending the outcome of her doping case.
* This story has been updated to reflect that Shayna Jack has been notified of the maximum ban and not banned already.