The 29-year-old had regularly impressed since taking over from Percy Montgomery as his country's first choice 15 and his enforced absence will leave head coach Peter de Villiers with some serious thinking to do before he announces his extended Springbok squad in less than a fortnight's time.
Of the leading contenders for the role now that Jantjes is unavailable, one player in particular will be familiar to a number of Lions supporters.
Stefan Terblanche played domestic rugby for the Ospreys between 2003 and 2007, making a total of 87 appearances for the Welsh region.
When the 6ft 2in full back cum wing moved to Wales it looked as though his international career had come to an end, yet six years on, it could soon be given a new lease of life.
Terblanche returned to his former province Natal 19 months ago and has since been a consistent performer in both the Currie Cup and Super 14, starting with a double try-scoring appearance and the man-of-the-match award in his very first game back in his homeland.
Despite being nearly 34 years of age, the ex-Boland player is now being touted as the man most likely to take over from Jantjes against Ian McGeechan's tourists next month.
If Terblanche does earn the nod from de Villiers, it would signal a remarkable turnaround in his international fortunes.
Terblanche won the first of his 37 caps way back in 1998, just a year after the Lions last toured South Africa. He went on to score 95 points for his country courtesy of 19 trie, having crossed the line four times on his international debut against Ireland in Bloemfontein.
Stefan Terblanche scored four tries on his Springbok debut in 1998
He would better that debut achievement just over a year later as he claimed a then Springbok record of five tries in a single game against Italy in 1999.
Terblanche's record in Springbok colours is truly outstanding, holding a ratio of a try every two games, a percentage only bettered in South African terms by legendary Boks Ray Mordt and Danie Gerber.
If the Mossel Bay native can repeat those kind of statistics if he does win a Springbok recall, then the Lions will certainly have their work cut out.
One thing that may count against him, however, is his age. Terblanche is clearly not a long-term replacement for Jantjes, yet with de Villiers and the whole of South Africa talking up the importance of beating the Lions, he could prove the most reliable option for three of the most-important Test matches in the Boks' recent history. And if de Villiers follows McGeechan's example and picks on form, then those in the know believe Terbalanche has to be the most sensible choice.
"They say Super14 rugby can be likened to Test rugby. Well, Stefan has proved himself at Super14 level," said former Springbok Theo van Rensburg.
"He has played outstanding rugby the last two seasons.
"Stefan kicks well and there is nothing wrong with his attacking game. He is also very good under the high ball."
Those views are backed by Cheetahs full back Bevin Fortuin who made his Springbok debut in 2006 but believes Terblanche should be the man to face the Lions in Durban, Pretoria and Johannesburg.
"His age should not count against him," said Fortuin. "He should be picked on form."
Terblanche is in line for a first international appearance since 2003
If de Villiers ignores those sentiments and decides Terblanche is too long in the tooth or that too many years have passed since his last international appearance then he could well give youth a chance to impress.
Two of South Africa's most-promising full backs, Zane Kirchner and Louis Ludik, are just 24 and 22 respectively and both are expected to wear Springbok colours at some point in the future.
Kirchner has impressed for the Bulls since joining from the Griquas in 2007 and has the advantage of playing regular rugby alongside almost certain Springbok starter Bryan Habana.
The George-born full back was called up to his country's training camp last year but had to withdraw through injury. He has since set his sights on achieving a secondinclusion, although he realises that the only way he can influence selection for the Test series against the Lions is to continue performing well for the remainder of the Super 14 season.
"I don't pick the side, so it's not in my hands," said Kirchner.
"What I can do is make sure I do my bit for the Bulls on Saturdays. That is the focus.
"It's always disappointing to hear of other players' injuries, but that that does not influence me. I believe I'm doing my bit for the Bulls, though there is always room for improvement.
"That call (to his first Springbok training camp) was good for my confidence because any player dreams of the jersey."
Zane Kirchner could be a star of the future and a star this summer
Like Kirchner, Ludik has also been named in just the one senior training squad, although he was a member of the Emerging Springbok side that won the IRB Nations Cup in 2007.
The Golden Lions star made his provincial debut four years ago and followed that with his Super 14 bow two years later. He is being talked about as a likely international starter in the coming seasons but de Villiers would certainly be placing a great deal of faith on the young man's shoulders if he was to give him his Test debut against Namibia later this month and then throw him in at the deep end against the Lions in June.
The inexperience of both Ludik and Kirchner is not a worry for former Springbok coach Carel du Plessis, however, as he believes both players have proved their worth this season.
"There is depth at fullback in South Africa," said du Plessis, who was at the helm when the Boks lost 2-1 to the Lions 12 years ago.
"Louis Ludik has been solid this season and Zane has had a few big games.
"Frans Steyn would also be an excellent choice at fullback ... it would be good to have specialists at fly-half and fullback who have been with the team in the past, but if that is not an option, Peter may have to look out for someone new."
When news of Jantjes' injury broke, Steyn was many people's choice to replace him in the Springbok side. The prodigious Sharks back may prefer to play at fly-half or inside centre but his strength under the high ball, superb kicking skills and his devastating attacking threat led many to see him as the perfect alternative.
Unfortunately for de Villiers, selection is never that simple.
Frans Steyn could miss the entire series against Ian McGeechan's Lions
Steyn followed Jantjes in picking up an injury that makes him highly doubtful for the first Test in five-and-a-half weeks time, although he could return in time for the second and third rubbers on the following weekends.
If he is ruled out of the Durban encounter, de Villiers will have a difficult decision to make. Does he bank on Steyn returning for the final two matches and pick a temporary replacement; does he rely on the seemingly safer option of reigniting the international career of Terblanche; or does he turn to the fearlessness of youth and plump for Kirchner or Ludik?
With so much resting on the outcome of the Lions tour and every single South African voicing an opinion, you can be sure that whatever decision de Villiers takes, it will be questioned left, right and centre all the way up until the Test series and beyond.