The All Blacks' 26-10 defeat in the Rugby Championship opener was their worst in 94 years in South Africa, triggering fresh calls in New Zealand for Foster to be sacked.
The three-time world champions have now slumped to a record low of fifth in the world rankings and head into their next match in Johannesburg on Saturday, August 13th, after a fifth defeat in six tests.
With a consecutive loss to the Springboks widely expected to make Foster's position untenable, the coach said players and staff needed to take a deep breath.
"We know there’s a lot of pressure on, and we’re feeling that. But our job is to look at our performance and how we can grow it," he told New Zealand media.
"I understand the frustration, but that doesn’t change what we have to do here.
"There’s no point sulking about it for too long. We’ve just got to get into Ellis Park and keep growing our game and still believe."
Many in New Zealand no longer believe in the team under Foster.
In a front-page editorial on Monday the New Zealand Herald, the country's largest newspaper, said Foster needed to go, calling him a "decent man who is out of his depth in a brutal business".
Foster's hopes of rallying his team at Ellis Park appear bleak with injury concerns over star flyhalf Beauden Barrett (31) and his fullback brother Jordie (25).
Beauden has a sore neck after landing heavily from a mid-air tackle by South Africa winger Kurt-Lee Arendse (26), who was red carded for the rash challenge, while Jordie left the field with an ankle injury.
Foster complained that Arendse had also clattered into Jordie Barrett unfairly as the All Black rose for a box kick in the 11th minute. Jordie was instead penalised for a knock-on.
Foster confirmed the All Blacks would be addressing South Africa's mid-air challenges with officials and said he expected more protection from them.
"It’s becoming a free-for-all for jumpers just to be able to jump and stick a hand out and say they’re competing. It needs to be addressed," he said.