Christie left the field part-way through the game against the Kings in Port Elizabeth in South Africa two weeks ago complaining of not feeling well.
He returned to New Zealand after the game - skipping the trip to Argentina - but it appears what happened to Christie and why is not exactly clear.
Highlanders coach Jamie Joseph confirmed there was not a complete medical answer at the moment to what affected Christie in the game.
He did not feel well during halftime and did not return to the field for the second half against the Kings.
"We don't know what happened in the game. He didn't feel well so we did a series of tests,'' Joseph said yesterday.
"Right now he [Christie] is out there doing some contact training but he wants to be part of final footy. So he is coming right.
"Last night he came up to me directly and said he was good to go. So that was a really good sign. But the medical answer is I am not quite sure. But he is firing. No-one really knows what happened.''
Joseph said Christie took a blow to the neck against the Kings.
"He took a hell of a knock to the neck and that is what really is keeping him out of this game. He puts his head and neck in some pretty tough places.
"I am not surprised he gets a few head knocks or neck knocks. But ultimately he is one of our captains and is itching to get back.''
Though Christie, who turns 31 later in the month, is out the side does welcome back hooker Liam Coltman, who has been sidelined since late May after injuring ligaments in his toe.
Joseph said it was good to get Coltman back - starting on the bench - but third-choice hooker Greg Pleasants-Tate had played well in his absence and it was a tough call to leave the Aucklander out.
Much flak had been thrown at the structure of the Super rugby competition this week but Joseph said in the end "it is what it is'' and the team just got on with playing.
In the end the so-called unfair structure of the competition could help the team.
"The competition is the competition. You accept it at the start of the year. You get on the treadmill at the start of the year and you don't seem to stop.
"For example, we could be on the plane again heading to South Africa. I guess what that means is it is not quite right for us. We are stuck down in Dunedin so we always have that extra flight. But what that does is it build resilience in your team, builds a real mental strength and you go from there.''