Anton Segner's injury situation has taken a more serious turn, with All Blacks head coach Dave Rennie admitting there is 'something brewing' after the 25-year-old loose forward was admitted to hospital for further assessment.

Segner was originally named on the bench for the first Test against the Springboks in Pretoria — which New Zealand won 33-16 — but was withdrawn hours before kick-off and replaced by Simon Parker. The All Blacks initially attributed the injury to a swollen ankle diagnosed as acute inflammatory arthritis, but Rennie was notably guarded when asked for an update ahead of the midweek match against the Lions at Ellis Park.

'There's nothing that I can really share at the moment,' Rennie said. 'He went into hospital for another check-up. There is something brewing, but I'll be a bit clearer by later tonight.'

Whether Segner returns home or remains in South Africa has not been determined.

Rennie also confirmed that prop Ethan De Groot and lock Josh Lord are ruled out of Saturday's second Test in Cape Town, both having left the Pretoria match with concussion and now subject to 12-day stand-downs. To cover their absence, Rennie called up prop Ofa Tu'ungafasi and lock Jamie Hannah, both of whom will feature off the bench against the Lions a day after arriving in South Africa.

'I sent Jamie a couple of messages, and we had to get someone to go around and knock on the door and wake him up to let him know he had about four hours to get on the plane,' Rennie said. 'They'll both be on the bench; hopefully they won't have to play too many minutes.'