All Blacks and Blues halfback Piri Weepu is undergoing test in hopsital after suffering a minor stroke at the start of March.
Medical staff have considered the stroke to be a non-rugby related condition and the 71-Test veteran will be out of rugby for at least four weeks as he recovers.
Weepu has been struggling with debilitating migraines recently, despite an MRI-scan appearing to give him the all clear to continue playing rugby.
Weepu is now undergoing testing to determine the cause of the stroke which appears to have occurred before the team travelled to South Africa in early March.
"Piri presented with transient symptoms that could have been from a migraine before he travelled and was cleared by specialists to travel, as long as he was monitored.He had no other symptoms to raise further concern while we were away," Blues doctor Stephen Kara said.
"We took the precaution of getting an MRI scan for him this week and we are thankful we are now getting to the bottom of this issue.
Weepu has had his fair share of concussions over a 10-year playing career, including a nasty one in 2013, but Dr Kara says they are not to blame for the migraines.
"Having spoken to Auckland City Hospital specialists, we are very confident that Piri's condition is not associated with any injury, in particular, any head injury," Dr Kara said.
The 30-year-old was last hit by a migraine during a team meeting and an hour later explained the effect they have on him.
"It's really annoying. Sometimes I'd be feeling a bit dizzy because of the headaches and things, having to sit down and take my time and feel better before I try anything else," Weepu said earlier this week.
"It's just trying to get over it really, during training. I've had it before games, leading into games the last couple of weeks, but when I'm out on the field it's basically auto-pilot."