Mysterious concussion symptoms are hanging over Hurricanes and All Blacks hooker Dane Coles - eight weeks out from the Lions Tour.
Coles sustained a knee injury when the Hurricanes played the Highlanders in March.
Hurricanes coach Chris Boyd said when Coles returned to training he got a calf strain and developed headaches.
"So he's being hindered not only by a calf strain but is now under a return to play protocol for concussion, the source of that is completely unknown by us so that's made it a bit more complex
"We don't know where he got those symptoms from, but they were not apparent to us until post his return to training from his knee injury, " Boyd said.
"We've had a look at the Highlanders game, which was the last game he played. He had no symptoms post that, so I'm not sure. The source of that is completely unknown to us."
Boyd said Coles is doing minimum training at the moment until his symptoms alleviate.
"We can't load his calf because he's getting headaches and in the end I'm not sure whether his concussion symptoms are going to go away first or whether his calf issue is going to go away first, but we can't test the calf until they do," he said.
Chris Boyd says with the cause of the concussion symptoms not clear- it's unknown when Dane Coles will return to the field.
Coles' is not the only All Blacks regular causing some concern as to whether they would be fit enough to face the Lions, who start their 10-match tour on June 3.
All Blacks captain Kieran Read has undergone surgery on a broken thumb and is out of action for up to six weeks, while fellow loose forward Jerome Kaino has had knee surgery and out of action for about the same period of time.