Retallick was cleared out in a ruck by Springboks opposite RG Snyman and landed awkwardly on his left shoulder. He was in visible pain as he walked off in the 61st minute of the 16-16 draw in Wellington.
Hansen did not give a timeline for his return to reporters on Sunday but sounded optimistic the former World Player of the Year would be fit to travel to Japan for the Sept. 20-Nov. 2 showpiece.
"Hopefully he will be available for the World Cup. He is one of our best players so that's good," the coach said.
The absence of Retallick would be massive blow to Hansen's plans for the World Cup, with Scott Barrett still on the sidelines with a broken thumb.
Hansen's depth in the second row falls away after Barrett with Patrick Tuipulotu having struggled to assert himself at international level in the past two years.
Jackson Hemopo has impressed in his four test appearances since he made his debut last year and is likely to partner Sam Whitelock against Australia in their final Rugby Championship match in Perth on Aug. 10.
Retallick, 28, won't be included in a New Zealand squad trimmed from 39 to 34 players to contest two Bledisloe Cup Tests. The squad is announced on Wednesday.
Hansen confirmed Sonny Bill Williams won't travel to Perth for the August 10 clash as he wants the veteran inside centre to play two provincial pre-season games in the next fortnight to improve his match fitness after a year dogged by injury.
Williams was patchy against the Springboks and later needed stitches to his nose but he has clearly done enough to survive the next cull, with Hansen targeting his selection for the August 17 Test at Eden Park.
"A guy that hasn't played very much rugby at all was obviously going to be rusty so I don't think we can get too judgmental," Hansen said.
"The fact his body held together was encouraging."
Hansen wasn't panicking about opening their season with two muddled Rugby Championship performances, having scraped past Argentina 20-16 and been outplayed in the first half by the intense South Africans.
"We haven't had a lot of preparation time so we knew that at times, with the new stuff we were introducing, that we were going to be a little off. And we were," Hansen said.
"There's enough signs to say that if we keep working away and get our timing and execution better, then we're going to hurt some teams."
New Zealand are second on the Rugby Championship table on six points after last night's draw with the Springboks, who have seven after they achieved a bonus-point victory over the Wallabies last week.