The Scottish champions' chief executive Peter Lawwell revealed the 24-year-old Israeli had signed after spending much of last season on loan to Liege's Belgian top-tier rivals Kortrijk.
Gershon could help fill the void left by centre-half Efe Ambrose while the Nigeria defender is on Africa Cup of Nations duty after becoming manager Neil Lennon's first January signing.
A statement read: "Celtic also has an option to make a permanent transfer of the player at the end of this (loan) period.
"Rami will join Neil Lennon's squad on their winter training camp in Spain, pending the completion of the appropriate work permit paperwork."
Meanwhile, Lawwell also revealed Central Coast Mariners midfielder Tom Rogic will join up with Celtic for a trial during their time in Marbella.