Dane Coles is the latest All Black battling fitness issues ahead of the British and Irish Lions tour, with the Wellington Hurricanes revealing Wednesday that the hooker has concussion symptoms.
Coles has not taken the field since he injured his knee when the Hurricanes played the Highlanders on March 18, then strained a calf muscle in training.
But what should be a straightforward recovery has been complicated by exercise-induced headaches that are a typical sign of a player with concussion.
Hurricanes coach Chris Boyd said the condition was a mystery, as Coles did not suffer an obvious head injury in his last match.
"The source of it is completely unknown to us and that's made it a little bit more complex," he told reporters.
He said Coles would have to pass concussion protocols before returning to play.
In the meantime, the headaches are preventing the 49-Test hooker from exercising enough to overcome his injuries, meaning he will struggle to be match-fit for the Lions.
The tourists arrive in New Zealand in early June and their first Test against the All Blacks is June 24.
Other All Blacks on the sick list are Kieran Read, Jerome Kaino, Ben Smith, Nehe Milner-Skudder, Patrick Tuipulotu, Elliot Dixon, Lima Sopoaga and Tawera Kerr-Barlow.