The Botswana international, who is currently on the books of Township Rollers in his homeland, linked up with Siwelele on Tuesday.
"Yes, he is here. He is training with us," confirmed a guarded Celtic CEO Khumbulani Konco.
Cameroonian shot-stopper Patrick Tignyemb is the current first-choice keeper of Jelusic.
Tignyemb is into his 10th year with the club, having amassed over 200 appearances for the side.
Meanwhile, Phunya Sele Sele have parted ways with wingers Khethokwakhe Masuku and Kabelo Mahlasela, and signed defender Lorenzo Gordinho and midfielder Menzi Masuku from Chippa United.
Gordinho was loaned to Celtic for a year as part of the deal that saw Mahlasela join Kaizer Chiefs.