Jantjies was the long-time deputy to regular number 10 Handre Pollard, including in their victorious 2019 Rugby World Cup campaign in Japan, but fell out of favour after several recent off-field issues and had not been selected since he was sent home from Argentina in September last year.
But with Pollard and Damian Willemse both recovering from injury and Manie Libbok the only fit fly-half in the squad, the Springboks have offered him a lifeline.
"Damian has a knee injury and will be touch-and-go (to play Australia), while Handre is definitely out," Bok coach Jacques Nienaber said in a statement on Thursday.
"It means Manie is our only fit fly-half as of today and we can’t go into a Test season without any cover. We weighed up the options available locally and overseas – having tracked all of them throughout the season just completed – and Elton is the next fly-half in line."
Jantjies was sent home from Argentina after media in South Africa reported that Jantjies, who is married, had earlier stayed at a guest house with Bok team dietician Zeenat Simjee. Both denied this was the case.
Jantjies was also arrested for "malicious damage to property" after an incident on an Emirates Airlines flight from Dubai to Johannesburg in May last year.
He joined French second-tier side Agen in November after his contract with Japanese side Red Hurricanes Osaka was ended abruptly in the wake of his axing in Argentina.
He has won 46 caps since making his international debut in 2012.
